A family of Microsoft word processing software products for creating web, email, and print documents.
If the date in the header should be displaying the current date each time, it will be a field code, and the date format displayed will be managed by a date-time picture switch. You can edit it to display it the way you prefer.
To edit the switch, right-click within the date and choose "Toggle Field Codes" (or press Shift-F9) to toggle from the result view to see the field code and the switch in effect. It will look something like this:
{ DATE @ "MMM d yyyy" } (this date format pattern would display "Mar 26, 2022" for today's date).
To display as 26 March 2022, edit the date format string to "d MMMM yyyy". To display as Saturday, 03/26/22, use "dddd, MM/dd/yy". If you used "YYYY-mm-dd", the date would display as 2022-03-26.
Finding details about the Date-Time Picture field code switch on Microsoft support pages is frustratingly difficult; instead refer to this description.