How to remove the overlap black areas from my mosaic

[Greta]

I want to remove the overlap black areas of my mosaic.

I manually reshape the boundary (red line) and this process removes the external black areas of my mosaic which is OK. I did the same process for the footprint (green line) but it does not work.. If I change the symbology as not data  I just get white space where the black space is. I want to see the underneath image if the first image has black areas. 

[JayantaPoddar]

Check if Build Footprint tool helps. Check the steps in How To: Remove black or white borders from rasters in a mosaic dataset .