When on the Files tab, you can choose Open in Sharepoint to open the web version of your Teams files:
This will open your default web browser, where you might need to log into your Office 365 account for the first time if you haven't done it before.
Once logged in, you will have the full layout of files for that Team, right-click the file where you need to revert to a previous version and select Version history:
A list of every modification to that document will show up, click on the small icon to the right of the version date/time so you can choose an option to:
1. View. This allows you to download an offline copy for review
2. Restore. Once you've confirmed this is the right version, you can have it overwrite the current one with this option.
3. Delete. It removes the selected version.