Did you already file the first original return? Was it accepted?
You can check your efile status here
When you efile you get back 2 emails. The first email only confirms the transmission. The second email says if the IRS (or state) Accepted or Rejected your efile.
If it was accepted then you need to mail in an Amended 1040X return to add more to it.
How to amend an Online return
Amended returns can only be mailed. It can take them 16 weeks for the IRS to process them. And they only mail checks for refunds. After 3 weeks you can track it here, https://www.irs.gov/filing/individuals/amended-returns-form-1040-x-/wheres-my-amended-return-1