Flip normals

Is there a way to flip surface normals?
I have a interior scan and if I export my model as .obj, I get a box around it. I belive it is because of normals facing outwards.
Any idea how to solve the problem?

Hi Clemens Rudolph
Use the bounding box (BBox) and set it a bit smaller than the actual BBox region and then use the FILTERING tool to get rid of it…
It is not about flipping normals…