Can't reset password for external drive

I have an M1 Mac Mini that boots off an external drive running macOS 13.5. I've forgotten the password, so I've attempted to reset it using the iCloud reset method, but that doesn't work. I finally noticed that it's because it's actually resetting the account on the internal drive. There's no option to reset the password of the account on the external drive despite that being the account I'm prompted to change via iCloud.

I have ssh access thanks to a previously shared key. From there I see that time machine backups are still working. Is there a way to reset the password via ssh without knowing the previous password, or am I going to have to bite the bullet and reinstall Ventura on that disk somehow and then restore the backup?