#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)(?<=notes:.*?)\b\d{1,2}([-\/])\d{1,2}\1\d{4}\b"
Local $sString = "wed and thurs and notes: are just so interesting 02-03-2019 on a new line please 04-05-2020 on another line please wed and thurs and notes: are just so interesting 02/03/2019 on a new line please 04/05/2020 on another line please"
Local $sSubst = "<br> $&"
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