if you mean the screw on the housing it won't make a difference. if you want a replacement you could probably get a screw set on ebay or aliexpress. chances are it won't stay in anyway if the screw fell out to begin with
connect the controller to a pc or laptop then open this site, https://gamepad-tester.com/. it will show you how bad its moving. if bad it needs the analogue stick replaced.
the nand (memory ic) is on the logic board, swapping 1 board over from 1 housing to another wont change anything you would be better just using the refurbished phone. you could replace the screen and flash via 3utools but select retain user data