If the returns were for a deceased person, you can submit an adjustment by mail using this CRA form: https://www.canada.ca/en/revenue-agency/services/forms-publications/forms/t1-adj.html
The interest is from an account from a deceased person. There were three executors and we each claimed a third of the interest. I took ten years to get everything settled because of a few complications. 2023 is the last year that I will have to claim this and I claimed the interest for all of the other years but when I was looking through my "stuff" for 2023, I realized I forgot 2021 and 2022. I was going to use the change return section of turbo tax, but thought that I would check to see if that's the best option.
If the interest needs to go on your return (not the deceased person's), then you can use ReFile to add the interest.