Android dump image file with no extension

Hi. I am completely layman with programming, and I am struggling with recovering smart phone data.
I tried to extract dump file using Oxygen forensic suite, but what i got is 'mmcblk0' 29GB file with no extension
and Oxygen Forensic result gave me anything what i wanted but only useless image files.
I don't know how to reuse 'mmcbl0' or amout virtual disk.
Is that file useless? can i add extension? or use somehow?
Please save me...