Please don't put it in all at once. It's best to be conservative when adding CYA and some other things. It's much easier to add more later than to take some out if you overshoot.

A CYA of 50 ppm is a good number to work with for most pools and the 9 pounds will get you close enough to it, either up or down a little but not enough so it would matter.

Put 3 or 4 cups worth in an old tube sock, knot the top or tie it off with a zip tie. You then fasten this in front of a return so the water hits it when the pump is running, or you can put it in the skimmer basket but it has to be done in such a way that it doesn't plug the hole and impede suction back to the pump.

CYA can be pretty slow to dissolve so this might take a couple of days.

What does the product container say about adding it? Does it say anything about pre-dissolving in a bucket of water? That's another method which works really well—but not all stabilizer products can be pre-dissolved.