How to unmount the dmg file after recovering formatted disk by Disk Drill?

Hi all,

Recently, I accidentally formatted my 500GB HDD hard drive. The drive was what left from my broken 2013 Macbook Pro 15". I tried to rescue the data by using Disk Drill and after roughly 4 hours, it recovered a file in .dmg extension which is almost 500GB, and put in under a folder named "HFS". I guess this file consists all the data I stored on my hard drive.

However, I could not do anything with this .dmg file now. I have try to open it with DiskImageMounter on my 2015 Macbook Pro Retina (MacOS Sierra 10.12.6) but nothing happen. Please, help.