Tables Missing In Wp Database – How Do I Restore My Backup?

After tinkering with my database and then trying to repair it, I’m told by WP that the _comments and _options tables don’t exist.

I have a backup of the database created immediately before the foul-up but can’t work out how to restore it.

Any page I try to go in the Dashboard tells me to repair the db.

I’d be grateful for any advice.