That’s not quite trivial for someone not familiar with exactly how it works, you’ll need to run these commands on the receiver you want to claim again:
Get new Feeder ID and change user account - #2 by wiedehopf
sudo systemctl stop piaware
sudo piaware-config feeder-id ""
sudo rm /var/cache/piaware/feeder_id
sudo systemctl restart piaware
Then with the new account and on the same network as the receiver this link must be visited:
PiAware - Claim and Link a Brand New PiAware Ground Station - FlightAware