I FILED MY SON'S 2015 TAX RETURN USING TURBO TAX I NEED HIS 2015 AIG BUT CAN'T REMEMBER THE USERNAME OR PASSWORD I USED NOR THE PHONE # FOR HIS ACCOUNT..WHAT TO DO???

The username is typically the email address but might not be. If you know the email address and still have access to it, you can reset the password on the login screen. If you do not know the email address/username, you might not be able to recover the account. If you know

You can however request a transcript from the IRS for his 2015 return here: https://www.irs.gov/individuals/get-transcript/