Hmm, it looks like the plugin is giving it a width of 700px instead of using max-width which makes it responsive.
You may have to ask their plugin support to see what has to be done to make it responsive in this case.
You can find our videos here: https://generatepress.com/example-videos/
We also have documentation here: https://generatepress.com/knowledgebase/
Let me know if you need more info 🙂