My rear rim is worn off by braking My rear rim had those small indents in it for rim brakes, they have brushed off now.
Can I re-indent those dots to make braking efficient again. My rim is double walled mtb compliant.
No.  That indent or wear groove is to indicate the amount of wear on the rim.  If you can no longer see the indent, it means the rim is worn and should be replaced.  Sheldon Brown's take.  It's similar to if you no longer had tread on a tire.  You couldn't re-indent the tire to make new tread.