This is unrelated to the previous problem in this thread so should have got a new one really - next time - please do new thread per problem !!
OK, what we have got there, I'm afraid, is an absolute disaster of a mesh, as revealed here by mesh checker, which shows how this mesh contains almost every type of broken polygon it is possible to make !
You have non-manifold edges, bad polygons galore, non-planars that shouldn't be there and coincident polys - it's a nightmare ! 🙂
This isn't worth saving - you need to start again. The selection and modelling tools cannot work predictably when they are dealing with this sort of mess. How you got into that state I cannot say ! 😕
CBR