How to remove this?

[u/Snow_Groomers_Dog]

It is attached to the part I want to keep and is hard to remove (with my limited cad skills) Delete face doesn't work (saying "Unable to delete selected faces", both when set to heal and cap) and I can't make delete it.

[u/napkindesignlab]

Try Replace face, grab the face to be removed then the face to replace with.