Hi During a screen replacement, the “male” part of this blue cable (i think it’s the antenna) did break off the mainboard...

You could do a hard reset. How to Hard Reset A Samsung Galaxy S7: (1) Turn off the Galaxy S7 (2) Press and hold at the same time:  Volume Up + Home button + Power button, until you see Samsung logo. (3) Then select from Recovery Mode menu “wipe data / factory reset” using Volume buttons to navigate and Power button to confirm. (4) Select “Yes — delete all user data” to confirm the whole operation. (5) After that select option “reboot system now”. Source: https://www.techjunkie.com/how-to-hard-reset-samsung-galaxy-s7/

You could replace them: Samsung Galaxy S7 Power/Volume Button Flex Replacement