Here’s the needed part [https://www.ebay.com/i/184376614600?|Canon AE-1 Program AL-1 Rewind Knob - Genuine Canon Part] You might be able to find the screw alone but its a custom part and a left hand thread to boot! A good camera repair shop may have it, sadly many shops have closed as film camera repair has dwindled.
To help you get it back together review this great vid [https://www.youtube.com/watch?v=NeVEwqn06b0|Quick Fix - Canon AE-1 Program/AL-1: Rewind Knob Assembly]