a few solutions that have worked for me on multiple occasions. We had bats that got into my GF's dorm multiple times senior year of college, I assume they lived in the building somewhere.

1) Open doors/windows to the outside if possible, close doors leading to other parts of the building, let it leave on its own

2) Use a net. Fishing net, pool skimmer, anything will work really. Get a piece of cardboard to slide over the net opening once you have it trapped. Take the bat outside and flip the net inside out, the bat should fly away