According to the Forms Availability table, the Form 1040X is currently projected to become available sometime on 2/27/2020. As we've seen before with this form, a date is subject to change.
When it's available, see this FAQ for instructions:
https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...
You should wait on any Federal refund (if applicable) to arrive first before amending.
In the meantime, do not make any changes in your original return. When amending, it must start off exactly as filed.
The amended return cannot be efiled. It must be printed, signed, dated, and mailed. When mailing, it's a good idea to use a method that has tracking such as certified mail, priority mail, etc.
Three weeks after mailing, it should show up in this IRS tool, where it can be monitored:
https://www.irs.gov/filing/wheres-my-amended-return
It can take the IRS about 16 weeks to process an amended return.
If you amend the Federal return, you may have to amend the state return (if applicable.)
See this FAQ:
https://ttlc.intuit.com/community/amending/help/do-i-need-to-amend-my-state-if-i-amend-my-federal/00...
