#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "^(DTSTART|DTEND);[^:]+:([0-9]{8})T000[01]00"
Local $sString = "DTSTART;TZID=Australia/Sydney:20230206T000000" & @CRLF & _
""
Local $sSubst = "${1};VALUE=DATE:${2}"
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm