I made an incorrect entry for sale of stock which has already been captured, while entering data. Now unable to remove this duplicate/dummy entry. How to proceed?

You will delete the duplicate information in the federal interview section. 

1. Select Income & Expenses 
2. Scroll down through all income until you see Investment income 
3. Select Stocks, Mutual Funds, Bonds, Other 
4. If you have any entries, you will see them on the following page titled Your investment sales summary.  If anything listed does not apply, select the trash can to the right to delete the input.

There is no trash can next to my investment summary...

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@Carroll Harsh wrote:

There is no trash can next to my investment summary...

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Are you using the TurboTax desktop editions on a Mac?  If so, there should be a grey scroll bar at the bottom of the Investment Summary window.  Scroll the bar to the right so the Edit button and the Trash Can symbol will be visible.