Host Bitwarden behind existing nginx reverse-proxy

i am a beginner with docker and nginx, so please keep that in mind.
I have managed to get my nginx Docker Container running with a paperless and a portainer container which are accessible via the nginx server.
I now want to migrate my standalone bitwarden server to this alreasy up-and-running system, but i cant seem to get bitwarden to agree not to spin up its own nginx, because i do not need it.
I have a subdomain and the corresponding ssl certificate ready, has anybody got that kind of thing up and running?
I would appreciate any help!

Thanks in advance and a warm greeting from cold Germany!