Are you referring to add it as blockchain sync peer?
In the troubleshooting manual I explain it how to add manually another node IP to sync faster your blockchain copy.
Enter SSH into your new Umbrel node, then:
cd umbrel
sudo docker exec bitcoin bitcoin-cli addnode "192.168.x.x:8333" "onetry"
replace “192.168.x.x” with your existing running node IP.
This will make your new node to sync directly from your old running node, without need to be connected to internet, if you have a slow connection or Tor is making problems.
Once is finished, you can remove the IP from peers and go back to normal connection.