I HAVE already mailed my return but forgot to put my bank info for direct deposit. How can I fix this?

You can change your banking info with the CRA. If you are in Canada or the United States, you can call the CRA at 1-800-959-8281. If you are somewhere else you can call 613-940-8495. Here are more ways to contact the CRA: https://www.canada.ca/en/revenue-agency/corporate/contact-information/telephone-numbers.html