I'm currently trying to fill in holes for this model part. The holes look like they're on flat surface but when I try to sketch on the surface to fill in the holes it says that it is a curved surface and cannot be sketched on.

So far I've tried:

• creating a reference plane on the front and extruding throughout the hole. This fills in the hole but it leaves an outline and I'm not sure if this is completely filling in the hole.
• creating two reference planes on the front and back plane and using intersect. However, this creates another error saying that these two planes cannot be intersected.

This is a completed part file that I received so there are no cut bodies or faces that I can just delete to get rid of the hole.

If anyone knows of a way to cleanly fill in or remove the holes that would be a lifesaver.

I've attached the model file below for anyone that wants to take a look.