Use these steps to go back to the section of your return to update your medical expenses:
On the top row of the TurboTax online screen, click on Search (or for CD/downloaded TurboTax locate the search box in the upper right corner)
This opens a box where you can type in “medical expenses, sch a” (be sure to enter exactly as shown here) and click the magnifying glass (or for CD/downloaded TurboTax, click Find)
The search results will give you an option to “Jump to medical expenses, sch a”
Click on the blue “Jump to medical expenses, sch a” link