You need to hold down fn1 + page up for a few seconds until the keyboard flashes red, then let go of the keys. Now you can use page up as the print screen key. If you hold down fn1 + page up for a few seconds again, it will go back to working as the page up key.

Just had to search this up and found out how to do this from a Reddit post, so I thought I'd put this information on here as well.