You could follow the bitcoin blockchain copy guide:
https://docs.start9.com/latest/user-manual/service-guides/bitcoin/blockchain-copy
But everywhere it says embassy-AAAAA, substitute in your umbrel. Substitute step 5 in that above blockchain copy guide for this part of part of this guide, where it says:
Optional: If you are also trying to skip having to do IBD on your Embassy, copy the Bitcoin blockchain data:
#Copy the blockchain from your umbrel to your local computer (this ~500GB transfer may take hours):
rsync -vr umbrel@umbrel.local:~/umbrel/app-data/bitcoin/data/bitcoin/{blocks,chainstate} ~umbreldata/bitcoin/
#Copy the blockchain data from your local computer to the embassy (this ~500GB transfer may take hours):
# IMPORTANT: In the next line, replace embassy-XXXXXXX.local with your embassy's hostname
rsync --rsync-path="sudo mkdir -p /embassy-data/package-data/volumes/bitcoind/data/main ; sudo rsync" ~/umbreldata/bitcoin/{blocks,chainstate} start9@embassy-XXXXXXX.local:/embassy-data/package-data/volumes/bitcoind/data/main/
You would replace embassy-XXXXXXX.local with embassy-BBBBBB.local, which of course would be your real embassy-adjective-noun.local name of the target embassy.