Hi Pirandos, you can have a better chance to see something very tiny like that if you switch the 3D view projection from perspective to parallel. That's under Options > View > "3D view projection" = Parallel. In a perspective view it can be difficult to see a tiny piece like that when you approach it because the near clipping plane will tend to cut it out.

The easiest way to get rid of that one is to delete the front face, then select the whole object and run Construct > Planar to make a new plane end cap.

There are a couple of small edge pieces at the bottom of the front face, it would probably be good to get rid of those. You can do that by running the Merge command ( https://moi3d.com/4.0/docs/moi_command_reference10.htm#merge ) after deleting the front face and before running Construct > Planar.

- Michael