If you have already filed, you will need to wait and see if the IRS Accepts or Rejects your Tax Return. 

• If the IRS Rejects your return, you will be able to make any needed changes and then resubmit your return. 

• If the IRS Accepts your return, then you will need to wait until the IRS fully processes your return and you receive your refund. Then you will need to Amend your Tax Return by filing Form 1040-X. You can click here for instructions on Amending your tax return: How to Change a Tax Return You Already Filed.

 [Keep in mind, the IRS has been processing some test returns, but they don't "officially" start processing returns until January 28, 2019.  Also, Form 1040-X won't be available until the end of January.]