Filing an amendment on already filed return due to TurboTax notification

I received following email from TurboTax after I already filed my return and received the refund:

Hi there,

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We’re reaching out to you because we’ve identified an error that might impact your 1099-INT data in TurboTax. The error isn’t with your Form 1099-INT itself, just the box 1 data TurboTax received. Please follow these steps to make sure the information in TurboTax is correct:

1. Sign In TurboTax
2. Open or continue your return
3. Navigate to Income then Investments and Savings to find your 1099-INT(s)
4. Select Edit next to your 1099-INT (if you have multiple, please check each)
5. Compare what’s in box 1 of a physical or electronic copy of your 1099-INT with what’s in TurboTax
   1. You might have multiple accounts on a single Form 1099-INT, so please make sure that the amount in box 1 is the total interest income from all the accounts listed on that form.

After following above steps, we confirmed that we missed reporting other 1099-INT interest incomes in other accounts.  How do we correct the misreported 1099-INT income? Do we edit the existing turbotax file or do we create a separate new turbo tax file to amend the previous one? This is the first time we are amending an already filed return. Please help.
Thanks