I had something very similar, I'd taken both wheels off to put the bike in the car to drive to a friend's place and when I reassembled it the back brake rubbed. In the end what I did was reposition the brake block very slightly. The way I did it (which was effective, if a little crude, and since I didn't have the user guide with me) was to slightly loosen both the allen bolts, apply the brakes hard, tighten the allen bolts, and release the brakes. The only tool needed was a 5mm allen key and it made a huge difference. Before the tweak if I lifted the back wheel and gave the pedals a fast quarter-turn push the wheel span maybe half a dozen times before stopping, after the tweak it kept spinning until I put the brake on.

As Old Hammer Boy said, make sure the wheel is properly seated first, otherwise you'll only have to readjust it when the wheel is properly seated.