It’s documented at https://hub.docker.com/r/duplicati/duplicati under “Preserving configuration”
https://hub.docker.com/r/linuxserver/duplicati has similar directions. Which Docker are you on?
Do you see any databases in the host volume? The settings would be in Duplicati-server.sqlite.
There are generally random-named job databases there too. I don’t use Docker myself though.
Any Docker experts out there, feel free to join in.