If you need to change a tax return that is already filed, then you have to file a Form 1040X to amend the filing. Just include the additional extension payment ...
If you have a copy of your 2018 tax return or if you filed in Turbotax last year, thats your best bet. Your AGI is on the first page. You can call the IRS (look...
In addition to the forms, make sure you attach all withholding forms (i.e. W2, 1099, etc). The tax authorities may adjust your return if the withholding documen...