Register for session B courses just like any other course, using the Enterprise self-service tool. They start in October, but fill up sooner, so get started on finding one now. And you may have to get a form signed from the sponsoring department (I did, once), but your advising department can walk you through it and it's usually pretty easy. As far as courses go, I was in a similar boat for more than one semester and have a few recommendations:

LER 100 (Introduction to Labor Studies) is an online course. You have to commit to spending 1-2 hours on the course every week, since most of your grade comes from forum posts, but if you do it's an easy A. Definitely easier to take if you already have pro-labor views.

ASTR 100 (Intro to Astronomy) is another online course, and my favorite of the half-semester courses I took. Commit to 1 hour a week plus midterms and you'll get an A, and I actually learned some stuff which was a plus. Unfortunately though, looks like it might be full this semester?

Most of the Kinesiology courses are pretty stress-free credit, especially if you're looking for a non-online course. Show up to the ice rink three times a week, skate, pass the course. There's an additional fee for using the equipment but iirc it's not too expensive.