Automated weeknumber

I’m trying to make an automated update of weeknumber in a cell but fail to make it work. Any ideas for a beginner at this?

What would be an automated update? Of what date? Triggered by what?

As a function of the TODAY() I have a schedule based on weeknumbers therefore I would like to update weeknumber automatically.

Sounds like =ISOWEEKNUM(TODAY()) would be your friend.