if it were me right now with Lemmy 0.18.4, I’d take the server offline, do a PostgreSQL dump file - keep a copy, then hand-edit the sequence numbers in the dump file - and do a restore.
you probably only had a few users, so I would set user to 100, person id can be higher because of federation - but jump ahead to 10000 maybe. Post and comment set ahead to 10000 … and community set ahead to 10000 because that gets federated
the PostgreSQL sequence numbers should only get used on newly created objects here-forward.