The rod is not supposed to turn.
The tensioner keeps pressure on the belt even when not fully tensioned (I told you the system was complicated) so don't expect the belt to sag as you loosen the tensioner.
Loosen the tensioner (#5) until it lifts off the bracket (#12). On my car, the tensioner lifts several cm off the bracket, but gets really difficult to turn before it comes off the rod. Be careful when you loosen the tensioner -- if the rod comes off the tensioner body, it takes some doing to get it back on. Press on the tensioner pulley (the small pulley beside the power steering pulley) until you can remove the belt.
Some people claim they can replace the belt without removing the fan. I must have two left hands.