how do I change the RMD I entered on turbo tax

As long as you have not filed your tax return yet, you will be able to go to the interview section of the program again and update your entries.

Follow the instructions here to get back to your 1099-R input section.  Select edit to the right of the retirement distribution that needs to be corrected.

Proceed through the input sections until you see a screen titled "About This Retirement Account." You will be able to adjust the amount of the RMD you received during the year on this screen. 

There will be another screen titled "Let's get more information about xx Required Minimum Distribution" which will confirm the amount of your RMD.  You will need to adjust the amount on this screen as well.