Ah, sorry - so, aside from seed phrase, you also want to save your lightning channels. It’s a little complicated to do it manually if you’re familiar with it (though instructions are available under this post, under “Recovering from a channels backup” - http://community.umbrel.com/t/frequently-asked-questions-faqs/32.
Umbrel also attempt to maintain a backup of your channels which can get restored if you need us to help.