After you file

The process for filing an amendment is straightforward. Simply file Form 1040X, Amended Tax Return, along with the corrected or additional documents/forms you did not originally file with your return. 

You cannot amend forms. You only can amend your tax return.

How to amend (change or correct) a return you already filed https://ttlc.intuit.com/replies/3288565

Video: How to Amend Your Tax Return https://turbotax.intuit.com/tax-tips/amend-return/video-how-to-amend-your-tax-return/L2wLEwRf1
IRS Offers Tips on How to Amend Your Tax Return https://www.irs.gov/newsroom/irs-offers-tips-on-how-to-amend-your-tax-return