Embed Youtube Thumbnails

Hello Rise community!

I am working on some courses in Rise and wanted to make the Youtube thumbnails (the image that shows when the video isn't playing) consistent among the courses. I uploaded those thumbnails to Youtube, however, the change did not reflect in Rise. The old thumbnails are still showing for me and I have deleted and re-added the blocks but it doesn't seem to change. Any tips on how to get the Youtube thumbnails to reflect on Rise as well? 

 

Thank you!

 

Isa