Hello there, Christine. You can’t unfile T4s once they are submitted, but you can correct them. After you file your original information return, you may need to make corrections to slips and file amended or cancelled slips.
You may want to visit these pages from the CRA for guidance:
You have clicked a link to a site outside of the QuickBooks or ProFile Communities. By clicking "Continue", you will leave the community and be taken to that site instead.