Lower the pH first, though using dichlor will lower your pH a bit.
You can use dichlor to start the process, it will add just as much chlorine as stabilizer (for every 1 ppm of chlorine it raises CYA by about 0.9 ppm). So make sure to track it carefully, assume your CYA will raise immediately even though it won't show up on a test for a week or two. I would ignore the trichlor, just save it for times you will be away for a couple of days. If you use all of your dichlor or add enough to get your CYA between 30-50 then switch to strictly bleach.
You can use dichlor to start the process, it will add just as much chlorine as stabilizer (for every 1 ppm of chlorine it raises CYA by about 0.9 ppm). So make sure to track it carefully, assume your CYA will raise immediately even though it won't show up on a test for a week or two. I would ignore the trichlor, just save it for times you will be away for a couple of days. If you use all of your dichlor or add enough to get your CYA between 30-50 then switch to strictly bleach.