You can file an amended tax return at any time after the original tax return has been filed and accepted by the tax authority, federal or state.
However, if you are receiving a refund with the amended return you have three years from the due date of the original tax return to file for the refund. After that date the refund will not be paid.
If you have taxes owed with the amended return then you should try and file as soon as possible since penalties and interest will continue to accrue until the taxes have been paid.
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-a...
