Form 1099-Rs are entered in a different area from the W-2s. If you already entered it as a W-2, then you need to delete it and go to the 1099-R section to re-enter it.
Use the following steps to go to that section of your return:
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 “1099-R” (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 1099-R”
Click on the blue “Jump
to 1099-R” link