Codesys V3.5 SP17 Patch 3 (64bit)
Pi package: 4.2.0.0
PFC200 package: 4.2.0.0

Here's my scripts for implementing local timezone for Eastern Standard Time - Toronto Canada.
Using UTIL Functions - getDateTime() and localDateTime()

1. Installed UTIL Library 3.5.17.0
2. Add declaration to Global Variable List
3. Created POU: prgTimeZone
4. Created Datatype: TimezoneInfo
5. Created custom Function: tzoneDOW
6. Created HMI screen
7. Changed Timezone setting in Global Variable List to test and verify.

1 Install UTIL Library

Library Manager > Add Library > UTIL Library 3.5.17.0

2 Global Variable List

GLOBAL VARIABLE LIST
code
~~~

VAR_GLOBAL CONSTANT
( Eastern Timezone declaration for Toronto, Canada.
DST begins on 2nd Sunday in March and EST begins on 1st Sunday in November by 1 hour.
Note: Ontario has two timezones - Central & Eastern
uiDay => 1..5 1=> first day of the month, 5 => last day of the month )

// Coordinated Universal Time
gc_tzTimeZoneUTC : TimeZone := (asgPeriod := [(sName:='UTC')]);

// Eastern Timezone - Toronto
gc_tzTimeZoneTOR : TimeZone :=
(
    iBias := -300,      (* -300 minutes => -5 hours difference with respect to UTC with GMT -05:00              *)
    asgPeriod :=
    [(sName:='EST',     (* Eastern Standard Time - EST begins on 1st Sunday in November at 3:00am - Fallback    *)
      dtDate := (uiMonth := 11, eWeekday := WEEKDAY.SUNDAY, uiDay := 1, uiHour := 3, uiMinute := 0)
     ),

    ( sName :='DST',    (* Daylight Saving Time - DST begins on 2nd Sunday in March at 3:00am - Spring Forward *)
      dtDate := (uiMonth := 3,  eWeekday := WEEKDAY.SUNDAY, uiDay := 2, uiHour := 3, uiMinute := 0),
      iBias := 60       (* minutes - spring forward 1 hour in March *)
    )]
 );

END_VAR

3 POU: prgTimeZone

PROGRAM prgTimeZone
VAR

utcDateTime     : ULINT;
localDT         : ULINT;
tZone           : ULINT;

utcDate         : DATE;
utcTime         : TIME_OF_DAY;
utc_eWeekday    : UTIL.WEEKDAY;
utc_sWeekday    : STRING(3);

localDate       : DATE;
localTime       : TIME_OF_DAY;
local_eWeekday  : UTIL.WEEKDAY;
local_sWeekday  : STRING(3);

errorID         : UTIL.ERROR;
period          : UTIL.PERIOD;
status          : STRING(8);

dst             : BOOL;
localTimezoneInfo   : TimezoneInfo;

END_VAR

( Set Eastern Timezone for Toronto, Canada - DST begins on 2nd Sunday in March and EST begins on 1st Sunday in November )

( Using FUNCTIONS: getTimeDate & localDateTime )

// UTC
utcDateTime := getDateTime();
SeparateDateTime(uliDateTIme:=utcDateTime,eWeekday=>utc_eWeekday,datDate=>utcDate,todTime=>utcTime);
utc_sWeekday := tzoneDOW(utc_eWeekday); // UTC Day of Week, 1= Mon, 2=TUE

// EST/DST
localDT := localDateTime(tzTimeZone:=gvl.gc_tzTimeZoneTOR,uliDateTIme:=utcDateTime,eErrorID=>errorID,ePeriod=>period);
SeparateDateTime(uliDateTIme:=localDT,eWeekday=>local_eWeekday,datDate=>localDate,todTIme=>localTime);

tZone := (utcDateTime - localDT) / (1000 * 3600); // utc-local time difference in hours
local_sWeekday := tzoneDOW(local_eWeekday); // Local Time Day of Week, 1= Mon, 2=TUE

( LOCAL TIMEZONE INFO - for HMI display purposes only )

localTimezoneInfo.est_iBias := gvl.gc_tzTimeZoneTOR.iBias;
localTimezoneInfo.est_sName := gvl.gc_tzTimeZoneTOR.asgPeriod[1].sName;
localTimezoneInfo.est_month := gvl.gc_tzTimeZoneTOR.asgPeriod[1].dtDate.uiMonth;
localTimezoneInfo.est_eWeekday := gvl.gc_tzTimeZoneTOR.asgPeriod[1].dtDate.eWeekday;
localTimezoneInfo.est_sWeekday := tzoneDOW(gvl.gc_tzTimeZoneTOR.asgPeriod[1].dtDate.eWeekday); // Function(tzoneDOW)
localTimezoneInfo.est_day := gvl.gc_tzTimeZoneTOR.asgPeriod[1].dtDate.uiDay;
localTimezoneInfo.est_hour := gvl.gc_tzTimeZoneTOR.asgPeriod[1].dtDate.uiHour;
localTimezoneInfo.est_minute := gvl.gc_tzTimeZoneTOR.asgPeriod[1].dtDate.uiMinute;

localTimezoneInfo.dst_iBias := gvl.gc_tzTimeZoneTOR.asgPeriod[2].iBias;
localTimezoneInfo.dst_sName := gvl.gc_tzTimeZoneTOR.asgPeriod[2].sName;
localTimezoneInfo.dst_month := gvl.gc_tzTimeZoneTOR.asgPeriod[2].dtDate.uiMonth;
localTimezoneInfo.dst_eWeekday := gvl.gc_tzTimeZoneTOR.asgPeriod[2].dtDate.eWeekday;
localTimezoneInfo.dst_sWeekday := tzoneDOW(gvl.gc_tzTimeZoneTOR.asgPeriod[2].dtDate.eWeekday); // Function(tzoneDOW)
localTimezoneInfo.dst_day := gvl.gc_tzTimeZoneTOR.asgPeriod[2].dtDate.uiDay;
localTimezoneInfo.dst_hour := gvl.gc_tzTimeZoneTOR.asgPeriod[2].dtDate.uiHour;
localTimezoneInfo.dst_minute := gvl.gc_tzTimeZoneTOR.asgPeriod[2].dtDate.uiMinute;

IF period = 1 THEN status := 'STANDARD'; dst := FALSE;
ELSIF period = 2 THEN status := 'DAYLIGHT'; dst := TRUE;
ELSE status := 'UNKNOWN'; dst := FALSE;
END_IF

4 Datatype: TimeZoneInfo(STRUCT)

TYPE TimezoneInfo :
STRUCT

est_iBias           : INT;
est_sName           : STRING(3);
est_month           : UINT; 
est_eWeekday        : UTIL.WEEKDAY;         
est_sWeekday        : STRING(3);
est_day             : UINT;                 
est_hour            : UINT;
est_minute          : UINT;

dst_sName           : STRING(3);
dst_month           : UINT;
dst_eWeekday        : UTIL.WEEKDAY;         // 1=monday 
dst_sWeekday        : STRING(3);
dst_day             : UINT;                 1..5 1=> first day in this month 5 => last day in this month
dst_hour            : UINT;
dst_minute          : UINT;
dst_iBias           : INT;

END_STRUCT
END_TYPE

5 Function: tzoneDOW

FUNCTION tzoneDOW : string
VAR_INPUT
eWeekday : UTIL.WEEKDAY;
END_VAR
VAR
END_VAR

( Local Timezone Day of Week )

CASE eWeekday OF

1 : tzoneDOW := 'MON';
2 : tzoneDOW := 'TUE';
3 : tzoneDOW := 'WED';
4 : tzoneDOW := 'THU';
5 : tzoneDOW := 'FRI';
6 : tzoneDOW := 'SAT';
7 : tzoneDOW := 'SUN';

END_CASE

6 HMI

see attachment

-krstech integration

Attached snapshots for your reference.
-krstech

What exactly is your question ⁉️😉💪