I've tried looking for tutorials on filling holes in blender meshes but I think my problem is a little different.
I have a hole in my model but not actually in the mesh.
What is the best work flow to fill holes then smoothing them in with the surrounding geometry?
I've tried grid fill but I often get an error asking me to select two edge loops, how do you do this?
Here I'm able to get a set of surfaces to fill the hole but ideally I'd like to give them some thickness, subdivide the faces then smooth everything out again?

