The usual problems are the mic not working and|or the USB port not functioning. Given the scarce availability a DIY by yourself or a friend may be possible. The following links how what can be done and even a repair shop may carry out the repairs.
You may be lucky and someone has one and there’s always the option to contact a #fairphoneangel to see if they may assist.
There are other topics but the above two show suffice.
@johannis contacted our “heaven”, but we’re not really close or big. So I gave the suggestion to make a more general request which has more reach and bigger chance of finding people. Since no one is close to him, any of the heavens would do, or someone just scrolling through the forum.