We currently don’t support this. But you should be able to do that with:
systemctl stop snap.lxd.daemon
LXD_DIR=/var/snap/lxd/common/lxd
rm $LXD_DIR/cluster.crt $LXD_DIR/cluster.key
sqlite3 $LXD_DIR/database/local.db "DELETE FROM config WHERE key='cluster.https_address'"
sqlite3 $LXD_DIR/database/local.db "DELETE FROM raft_nodes"
This is from the top of my head, I didn’t test it. If you try it, please backup those files first.