Yes, you should be able to Edit your 1099-R entry in TurboTax.
On the 1099-R Summary Page, if you're in TurboTax Online, you should see a screen with a pencil icon to the left of the trash can to click on to Edit (screenshot).
Also, if you're in TurboTax Online, try clearing your Cache and Cookies, then re-try your Edit.
In TurboTax Desktop, the buttons on the 1099-Summary Page are labeled 'Edit' and 'Delete', or you can make changes directly on the 1099-R form in FORMS mode.
If you can't resolve your issue, here's how to Contact TurboTax Support.