reset the users roles – is there a way to do this?

The easiest way I know to reset roles and their associated capabilities is to use wp-cli.

wp-cli has a built-in method for resetting roles. You can specify any that you want to reset. For example:

wp role reset author contributor editor subscriber

There is also an --all flag, which you can use like this:

wp role reset --all

Warning that this will include resetting the administrator capabilities, which may remove access to some plugins, so use with caution.