If i have already filed and than recieved another form in mail can i still add to my tax return.?

If your income tax was E-Filed and Accepted by the IRS you will have to wait for the IRS to process your income tax return and you will have to Amend your return. 

If your income tax return was rejected by the IRS, you can add the missing information and E-File your income tax return.

See the TurboTax FAQ for additional information:  https://ttlc.intuit.com/replies/5170475