Whether you prepared the return or not, you can use the program to (a) prepare a 1040 that matches what was filed, then (b) go through the steps to prepare a 1040X. 

You should find all the steps you need here. https://proconnect.intuit.com/community/federal-taxes/help/how-do-i-efile-a-1040x-in-proconnect-tax-...

If you really want a blank 1040, here you go https://www.irs.gov/pub/irs-pdf/f1040.pdf