Easiest way to add listings to a new subcategory?

I discovered mid-stream that I need to add a new subcategory for usability reasons. I have 105 listings and it would clearly take a lot of time to open Edit Listings and check each subcat box.

What is the best way to add perhaps 50 listings to the new subcat?

My problem is, I have never in my life raised the hood on a MySQL database.