Valheim
Before you start
World Saves
Your world saves will be stored in the path ./user if you use the provided docker-compose.yml.
This will allow you to download/backup/move files around at your leisure.
Manually Configuring Settings
You can go to the official docs to see what you can change. Just replace the config files with what you want and restart the server.
All of these files can be found and edited in the server's local storage path.
./peon/servers/[game_uid]/[server_name]/
Stand-alone mode
Or... just use PEON. it should do all the heavy lifting for you.
Links
If you want to dig a bit deeper, here are the links