You can follow the advice already posted on this threadHi,
I am in the same boat where I was refused a study permit as a minor, then came to Canada on a study permit. I now have a PGWP and have gotten my ITA. I had completely forgotten to disclose this refusal. Could you please provide any advice on how I should phrase this to IRCC. I had no intention of misrepresentation.
Any help would be appreciated.