Hey ,
In order to set up your character or NPC to flying, you’ll first need to make sure the Character Movement is set to the speed you’d like it to be while flying. You can see that by simply clicking on your Character Blueprint. Then, you’ll want to check the box in Movement Component for Can Fly.
You may want to look over some additional tutorials, especially if you’re making NPCs and are going to be using navigation meshes.
Below are a few tutorials or documentation I’ve gathered for you:
- [Navmesh Content Examples][1]
- [Creating Nav Mesh Bounds Volume][2]
- [ NavMesh Search][3]
- [ Flying AI Search][4]
Hopefully one of the tutorials will assist you with creating AI that fly around your map.
Cheers! 
Content Examples Sample Project for Unreal Engine | Unreal Engine 5.1 Documentation
[2]: https://docs.unrealengine.com/latest/INT/Engine/AI/BehaviorTrees/QuickStart/2/index.html
[3]: https://www./results?search_query=unreal+engine+4+navmesh
[4]: https://www./results?search_query=unreal+engine+4+flying+ai