You may not be in the right place to enter your Social Security benefits income. Try going to Wages and Income > Retirement Plans and Social Security > Social Security (SSA-1099, RRB-1099) and click Start or Update.
See the following TurboTax help article for more information:
Where do I enter an SSA-1099, SSA-1099-SM, or SSA-1099-R-OP1?