If you mean this mod: https://www.beamng.com/threads/blue-bird-yellow-school-bus.17438/ It's marked as outdated, means it will not work properly in the newer version, unless the author or somebody fixes it.
The mod has been dead since 2017. But maybe this is a good replacement. https://www.beamng.com/resources/dansworth-d1500-type-c-front-engine-bus.110/
There's also this one (which used to be the Blue Bird bus): https://www.beamng.com/resources/dansworth-d1500-type-c-front-engine-bus.110/
Uh yeah. I wonder how i didn't knew about that mod at all. Its so different from the one i posted too! No. You shouldn't. What is your new problem.