Mass edit entry author?

I’ve just imported a batch of entries from Movabletype. Some of them were assigned to a newly created author #2, the majority was assigned under newly created author #3. I’d rather switch them all to author number one (site admin). Is there a way to change their author en mass, or do I have to do it manualy, one entry at a time, in the database? I’ve done the manual way before, and I needn’t say it’s highly boring and inefficient.