I forgot to file second return. First return accepted and deposited. What should i do ? Can i amend the return ?

One more return?  If you are filing your own tax return there is only ONE tax return to file.  If you received W-2 or some other form for 2020 then you have to amend the original tax return that was filed to add that form.

If the return is accepted you will have to amend your original tax return. An amended return, Form 1040X, can only be printed and mailed to the IRS if the original tax return was not e-filed. The IRS will take up to 16 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 on amending a tax return originally completed and filed using the 2020 TurboTax online editions - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/01/27577

The IRS Form 1040-X for amending a 2020 tax return is scheduled to be available on 03/25/2021 (subject to change)