There is a pulley that puts tension to the belt. It is spring loaded and does not need adjustment. When removing old belt, I just pulled the tensioner pulley by hand to loose the belt. Same when replacing the new one
they are wrong from factory, the rear axle needs to go down about 1cm to get the pulleys to align. if you take out the rear "bumper" you will see that the engine pulley and the pulley on axle are not level.
I moved the axle down with 4 M12 nuts, longer M8 bolts for the axle. Then you need to fabricate a small bracket infront of gearbox that is about 10mm higher. Not that hard to do. Acually i did this operation 2 days ago. (Changed engine due to the oildrain hose had a crack, oil leaked out and the rod decided to say "peekaboo") so inspect the oildrain hose at the same time... crap quality