Do not include your old 1040 nor your revised 1040 because the Form 1040-X reflects any changes there and becomes your new tax return.
To claim the rebate credit , put $1,400 on 1040-X Line 15 Col B and Col C
Check the "other" box and write "rebate credit" in the space provided.
after doing the arithmetic for the remaining lines, you would get a 1040-X refund of $1,400
You can do this all yourself by getting an editable PDF Form 1040-X from the IRS website.
@Edwin Calica
