The problem is that you modelled the entire room and exported it as a single mesh. When you imported that into unreal, it created a box collision around the entire mesh. Double click the model (to bring up the model editor), clear the collision model, and start adding in custom collisions.
edit: Since I had to do some work on my stuff, here is what I’m talking about:
This is what the default import should look like - mileage and model dependent of course.
://i.imgur/GtyzBfw.png
And here is a better version of collision so our player(s) can actually traverse the model:
://i.imgur/ByqvEce.png