First finish entering all of your income. Then click the Search button at the top and enter "medical expenses" (without the quotes) in the search box. Click the magnifying glass, then click the link that says "Jump to medical expenses."
BUT -
1. The amount that you actually get to deduct is only your unreimbursed medical expenses in excess of 7.5% of your Adjusted Gross Income (AGI). Enter the full amount that you paid that was not reimbursed. TurboTax will subtract 7.5% of your AGI.
2. Medical expenses are an itemized deduction. They will not make any difference in your tax unless your total itemized deductions are more than your standard deduction.