How do I erase the contents of 1099-INT box 15. I accidentally entered a value for State and I did not mean to.

You can either simply delete this Form 1099-INT and re-enter without box 15, or go in and edit the current form. 

In TurboTax Online, please sign in and

1. Select  Federal, on the left menu bar
2. Click on Wages and Income, at the top
3. Scroll down to the Investments and Savings sections and click on Show More
4. For Interest on 1099-INT click on Revisit
5. Scroll down to your Form 1099-INT and either
6. Click on the trash can icon to delete
7. or select Review

I have done all of that. The problem is that when you go back to that 1099-INT form for a given bank, you cannot modify Box 15 if it is already populated with the state that I accidentally entered and would like to delete. Yes, I can delete this 1099-INT and reenter it but I would rather not. 

As painful as it may be in your case, it will probably be faster in the long run to do as Teresa says: just delete it and re-add it. 

The trash can function to delete a particular 1099-INT entry not work?  I created an entry and now want to delete it and upload the 1099-INT using a different method, but turbotax (trash can) isn't working.  I click on it and nothing happens.  Any advice?  BTW, I'm using the desktop version of turbotax.

If you are on the desktop version of TurboTax, go into the FORMs mode.

1. All of the forms in your return are listed on the left side.
2. Click on and select the form you want to delete.
3. Visually verify that is the one you want to delete.
4. At the bottom of the page select [Delete Form]
5. Are you sure - Yes
6. Return to Step-by-Step
7. Continue posting your tax return.

@Taxtasks