Set it for campden tablets and white wine, fill in the pH and volume of your cider, and hit Calculate. After you hit the calculate button, it will tell you the recommended SO2 level for that pH. Rerun it with that target to get the actual addition.
For sorbate, follow the directions on the package.
The two additions work pretty fast, but I’d give it at least a couple days to a week to be sure before adding the concentrate.
To figure concentration volume, do bench trials. Put 100 ml of cider in each of four glasses, then use a medicine syringe to put 5 ml in the first glass, 10 ml in the second glass, and 15 ml in the third glass and 20 ml in the fourth glass. Mix and taste to figure out if one of these is what you want, or if you want to be in the 5-10 range, 10-15 range, 15-20 range, or sweeter. You can then do a finer trial to key things in more precisely if you want. Once you figure out how much concentrate to add per 100 ml cider, scale that up to figure how much for the full batch.