First, you will want to wait until your tax return is accepted or rejected. If it is rejected, then you can go in and fix the mistake and add the 1099-MISC. If accepted, then you will want to wait until your original tax return is processed by the IRS. If you are receiving a refund, you should wait until the check is issued. Amended returns must be filed by mail.
To amend a 2017 return, follow the steps in the article below (The 2017 amended tax return instructions will be available sometime in late January/Early February):