Just filed my return but later found a 1099-DIV form which I forgot to add to returns. It is new this year. How can I do a corrected tax return?

You will have to wait for the IRS to either Accept or Reject your filed federal tax return.
If the return is rejected you can make the necessary changes and e-file again.
If the return is accepted you will have to amend your original tax return. An amended return, Form 1040-X, can only be printed and mailed to the IRS if the original tax return was not e-filed. The IRS will take up to 20 weeks or longer to process an amended tax return.

Before starting to amend the tax return, wait for the tax refund to be received or the taxes due to be paid and processed by the IRS.

See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-already-filed/L4VjJ9BA2_US_en_US?uid=ld1n99kr

Yes, you may have to amend your tax return.  However, the IRS may pick up on the missing 1099-DIV and recalculate your return.

For that reason, you will have to wait for your return to be processed.

To amend your return:

 

• You will have to use the same TurboTax account that you used for the original tax return.
• Once you begin your amendment, you'll see your original return. 
  • The refund calculator will start new at $0 and only reflect the changes in the refund or tax due
  • Only make changes to the areas of your return that need amending.
• You have three years from the date you filed your return or two years after you paid the tax due (whichever is later) to file an amendment.

 

Sign in to TurboTax.

1. On the home screen, scroll down to Your tax returns & documents and 
2. select the year you want to amend.
3. Select Amend (change) return, then. 
4. Amend using TurboTax Online
   1. If you're told to amend your return via TurboTax Desktop, follow the steps for TurboTax CD/Download below instead.
5. On the screen OK, let's get a kickstart on your amended return, select the reason(s) you're amending and continue.
6. When you reach Here's the info for your amended federal return, select Start next to the info you need to change.
7. Continue through the screens, make the changes you need to make, and carefully answer the remaining questions to finish amending your return.