If it is a video course and quiz here on IDEAfit TV, you can go to your
“My Account” tab by clicking on your picture in the upper right hand corner of any page when you are logged in. Then just a little ways down that page is a line of clickable things, pick “My Education” and click it. On that page you will find a list of courses you are enrolled in and courses you completed. In the completed list you should be able to find any completed quizzes. They stick around on that list a long time. I have some from back in 2011 on there still.
If that doesn’t work for some reason, contact IDEA directly. Contact info is at the bottom of every page of this site as well.