If you itemize deductions, you can include out-of-pocket costs for supplemental medical insurance. There is a screen in the medical expenses section of TurboTax just for insurance premiums. (Click the screenshot below to enlarge it for reference.)

• Open (continue) your return in TurboTax Online. (If your return isn't open, you'll need to sign in, click Take me to my return, then click Pick up where I left off.)
• Click My Account (top right of your screen).
• Select Tools.
• In the pop-up window, select Topic Search.
• In the search bar, type medical expenses.
• In the results box, highlight medical expenses, sch a, then click GO.
• Follow the onscreen instructions. Note that medical expenses are divided into numerous categories, so you will go through several screens before you get to the the medical insurance premiums screen.