The video lessons can be viewed from your student's account that you set up from your parent account. Log in with your student's credentials and pick any lesson. Select the "Video" tab to view the videos.
If you don't see a Video tab, then that means a video has not been released yet for that lesson and/or book. Here is the regularly updated video release schedule: https://www.mymathassistant.com/video-lesson-release-schedule/
If the videos do not seem to load correctly, make sure that you don't have anything on your internet filter that is filtering out "player.vimeo.com".