You can add the stabilizer either by pouring it slowly into the skimmer, then not backwashing or cleaning your filter for at least a week, (it takes a long time to dissolve and start showing up as a testable level in the water, so don't bother testing for it for 4-5 days, either) or put it in an old sock or knee-hi and either put that in the skimmer or suspend it in front of a return.
Follow the instructions on the container for the amount to add--you want to shoot for 20-30 ppm at first, then you can adjust it from there.

To lower your pH (and alk) you can either use dry acid (labeled pH down) or liquid muriatic acid. The muriatic is cheaper and more efficient, but be very careful not to get it in your eyes or on skin, and don't breathe the fumes from the container. I'd start with about 3/4 cup of acid, pour it slowly into the return stream, then give it a few hours to circulate and retest. Keep going til your pH is 7.0, then stop adding acid and begin to aerate your water so your pH will come back up without raising your alk. I would strongly advise you to wear gloves, glasses, and old clothes!

Janet