How do I ammend my Middle Initial on my tax return that I already files?

If the IRS accepts your tax return there should be no need to amend the return for the middle initial.  Only if the IRS contacts you by mail in the future concerning this would you need to amend

There is no need to go through the trouble of amending your return to change your middle initial. As long as the first and last name and social security number is correct there shouldn't be a problem with processing your return. Wait until next year's filing to make the change.