I just received a 1099-NEC on March 30, 2024 for 2023. I have already filed my taxes. Looke like they mailed it on Marhc 26, 2024.What do I do about this?

You don't need the actual 1099NEC to file.  Did you include the income on your Schedule C?  If not you need to amend to add it.

You should not amend until the first return has fully processed and you get the first refund or your tax due payment has cleared.  

How to Amend this year

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-federal-tax-return-current-year/L7eS6o1qh_US_en_US

it is late to receive your tax document, however as indicated by VolvoGirl, you do not need to be concerned if you already claimed all of your business income from self employment.

If you need to amend you can do so now: Be sure to read all the instructions carefully, before you begin, so that TurboTax knows the original numbers and the changed numbers for your amendment.

• How to amend (change or correct) a return already filed?
• What is the deadline for filing an amended return?
• How to file an amended return with the IRS

@lsellers1