In the polygon tab there should be Reduce > Merge > Unify? If not you can select one poly by clicking on it (that'll select both overlapping polygons) then hit the down arrow key to deselect the last selected polygon, leaving you with just one, which you can delete.
Hi Dear, I tried the radial array with merge vertexes options. However I accidentally duplicate 4 times instead of 3. The duplicated overlapped so I did not recognised it in time. So it seems that there are faces overlapped while they have 4 vertexes. If I try to double click one of the boundary edges it only selects that…