Installing vapor barrier from the backside of the wall

I live in a 1940s cape cod so there is a small attic area on each side of the upstairs bedrooms. The upstairs is obviously poorly insulated, gets very hot in the summer and cold in the winter. What I found is that the walls between bedroom and attic appear to have been insulated from the back after the drywall was up. The insulation (very thin, low r value) is stapled to the studs on the attic side leaving a 3” airgap between the drywall and the vapor barrier. What is the best way to correct...

Installing vapor barrier from the backside of the wall