The software will calculate it automatically. Just enter your 1099G and the software will calculate how much--if any-- of your unemployment is taxable.
You will have to enter a 1099G that is issued by your state.
Some states will mail out the 1099G. Or you might need to go to your state’s unemployment website and use the password, etc. that you have been using to certify for weekly benefits to get your 1099G from the state’s site.
Enter your 1099G in Federal>Wages & Income>Unemployment
Go through the screens very carefully, making sure to enter any federal/state tax you had withheld from the unemployment.