Hi,
i tried to select the points and pressed fill hole but it doesnt work.
I cannot figure out how to add a simple face inside this mesh.
When I want to fill it tells me that my current selection cannot be filled.
So how can I add a face there, cause in blender its quite easy.
Hope you can help me out 
Did you ever figure it out?
Hi yeah i did, you must change the selection filter to vertex (the middle option) and after that you select 2 of the 3 vertex/lines where you want to create the missing face. The both lines must attach each other otherwise this wont work. After the selection you click the Bridge Option under Edge Edits.
If you need some pictures just write another reply.
Thanks! I ended up just remaking the model from scratch instead lol. But will try if I need it in the future
