What I would do first is close the game immediately, prior to the next autosave happening.

Then, you can check if you have a suitable auto-backup world file. (Check date and time of the file). Typically in a folder such as:
C:\Users\YourName\AppData\LocalLow\IronGate\Valheim\worlds

However, since cloud saves are used, I am not sure how that would work. Probably other people can help more than me. ;p