You don't have to do anything. When you enter your 1099-G for unemployment, TurboTax will automatically give you the $10,200 exclusion. The exclusion will appear on Schedule 1 line 8.
If you have already filed your tax return without the exclusion, the IRS will recalculate your tax return and send you the additional refund for the $10,200 exclusion. It might take several months to get it. DO NOT file an amended return. For details see the following IRS announcement.
You do not deduct it. You just enter your 1099G and let the software do the calculations. The software is all up to date for unemployment and will calculate how much--if any--of your unemployment is taxable.
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.