Is it possible that the old primary follow the new secondary?
On postgresql12:

systemctl stop postgresql-12.service

/usr/pgsql-12/bin/repmgr -f /etc/repmgr/12/repmgr.conf node rejoin --force-rewind --verbose -d 'host= psql02 user=repmgr dbname=repmgr connect_timeout=2' --dry-run