Since the return is attached to the 1040 X, you need to first recreate the return as filed.
https://accountants.intuit.com/support/en-us/help-article/amend-tax-return/amend-individual-return-1...
For others searching for this information https://accountants.intuit.com/community/proconnect-tax-idea-exchange/originally-filed-return-versus... can add some training.
