To lower pH and TA together (mostly the pH), you just add the acid any way you like, but SLOWLY since it can be harmful (I pour slowly over a return where the skimmer is on the other side). For extra safety, you can add the acid to a bucket of pool water and then pour that in slowly.
To lower the TA, use the procedure described in this post
. Aeration at low pH and adding acid to keep the pH low is the fastest way to lower the TA. Using an air compressor with a nozzle or pipe that produces lots of tiny bubbles works really well as do contraptions that pipe water from returns into shower jets to create bubbles. Get creative! It's fun.
As for how much acid lowers how much TA, it's not a simple formula, but if you give me the starting pH, TA and CYA and your goal pH and TA, I can tell you how much is needed for each step. I have a (complicated) spreadsheet that calculates this accurately (found here