hi
like in the video, put your ratchet in the square, usually easiest if your ratchet is in line with the tensioner
so with the ratchet pointing straight up, push it to the left, anti clockwise, no need to touch the nut, pulley will move a least 1/2" to a 1"
there will be spring tension, I use a power bar, 2 foot long, makes it easier
and the tension will slacken, I would push the belt back towards the engine off the tensioner pulley
then you can release the ratchet
turning it to the right, clockwise, your just pushing against the belt, it would not move
cheers
Joe