I have already received my tax return, but forgot to include my ssa-1099 on the previous federal and State return. What do I need to do now?

[bluedeb]

You would have to amend your returns in order include your SSA-1099 form.  

How to amend (change or correct) a return you've already filed

https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...

[MayaD]

You need to amend your return and report your SSA-1099 social security form.

You may have to pay taxes on Social Security benefits. It depends on the amount of your income from all sources, and your filing status

Is my Social Security income taxable?

1. In TurboTax, scroll down to Your tax returns & documents. Select Show and then select Amend (change) return, and then Amend using TurboTax Online. (If you don't see Your tax returns & documents, select Tax Home on the left.)
2. Select the reason you’re amending and follow the instructions

To report your Social Security Income:

• Select Federal from the left menu
• Go to Wages and Income then Income and Expenses.
• Scroll down to Retirement Plans and Social Securities.
• Select Strat next to Social Security (SSA-1099, RRB-1099)