Hi @TAC you may want to confirm on mempool.space whether this transaction has RBF flags or not.
After SSHing into your node, you can run the following command with your transaction info to bump the fee
sudo ~/umbrel/scripts/app compose lightning exec lnd lncli wallet bumpfee --sat_per_byte <number of new sats> <txid>:<index point> (index point may be 0 or 1)