When you go through the medical expenses section of TurboTax, you'll reach a page that asks How much did you spend on insurance premiums? Add the amounts you paid for Medigap and prescription insurance (not shown on Form SSA-1099) and enter this total in the Medical insurance premiums box. (Click the screenshot below to enlarge it for reference.)
The FAQ below tells you how to get to the medical expenses section in TurboTax.
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