I’m not sure what other way the CRA agent may have suggested, but if you need to change your 2021 return to add your GST/HST number, you can do so here: TurboTax Online 2021. Login, then click the Refile button next to the return you want to adjust. Click “Find” (magnifying glass) and search for “self”. Then select “Self-Employment” from the list and click on the “Go” button to get back to the Self-Employment section.
Yu would also need to do a GST/HST return if you haven’t already done so. You would have to fill out and submit one through the Canada Revenue Agency (CRA) website. You can read more about it on this CRA page: https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/rc4022/general-info...
If you are audited, just be sure to have all your receipts and other records ready. When the CRA does an audit they are just will double checking that what you have matches with what you have put on your tax return. You can read more about getting audited in this TurboTax article: https://turbotax.intuit.ca/tips/what-small-businesses-should-know-about-the-audit-process-6134
Please note: As of Friday, January 27, 2023, at 11:59 p.m. EST, the Canada Revenue Agency (CRA) will temporarily close all NETFILE, REFILE and EFILE transmissions. The services will resume on Monday, February 20, 2023.
