You can't stop the process. Once you submit the efile it's just like dropping a mailed return into a post office box. Your return will be held in the TurboTax servers until the IRS pulls it starting on Jan. 28. The IRS will then either accept it or reject it. If rejected, you can then make the necessary changes and resubmit the efile.
If accepted, you must wait until the IRS processes your return and sends you the refund. Then you can begin the process to prepare, print, sign, and mail an amended return form 1040X to make the changes. Do not make any changes to your original return until you begin the amended return. The 1040X is estimated to be available on 1/25/19. After completion, it must be mailed. It can't be efiled. The IRS takes about 16 weeks to process an amended return.
