There are backup files in C:\Users\Your Name\AppData\LocalLow\IronGate\Valheim

There's separate directories for "worlds" and "characters". The backups are the .old files. You should backup the whole Valheim directory before messing with it. Take off the .old and see if that helps. Maybe you know all this, but if you don't, hopefully it will help.

Edit: Hopefully you didn't just make a new character.