How to make a simple Flying AI, stay on the same height level

Hey guys, yet another time i need help.

Im trying to get an Flying AI done, which should simply fly around on the same height level. I dont know how i archieve this kind of thing. I searched for tutorials, but everything i see is so complex i dont get into it.

Like i said, it doesnt need to fly up and down yet, just get a random location within the level and patrol.

Adjusting the capsule to make it look like its flying wont help me, since it would avoid every mesh and move around it as far as i know.

So is there anyone can help me in a way or another ?