SOLVED: Lost admin account

[TheDreadPirate]

Stop the container, open a file browser and go to the directory you mounted /config. In /config there will be another config folder. In there is a file called system.xml.

Open that file in a text editor. There is a field called "IsStartupWizardComplete". Set that field to false and save. Start the jellyfin container.

In an incognito browser window, navigate to your jellyfin server. It should prompt you as if it was a fresh setup. Don't worry, your data is fine.

Create a new username and password and it should overwrite your existing admin user's name and credentials. This WILL NOT overwrite any watch status.

Once you've done that, just click next and skip the remaining prompts.