I have supplemental income paid separately than salary, included in W2 box 1. How do I enter my taxes so that my supp income is taxed at 22% not regular income tax rate?

Anything in box 1 of your W-2 is taxed as ordinary income . The 22% rate, you may have heard of, is just for withholding purposes. At actual time, it's taxed at regular rates.

see https://www.businessinsider.com/why-bonus-taxed-high-2014-12)