Can't find the clip, but Jonathan frakes told Patrick Stewart that he had to see Galaxy Quest, and that he had to see it in a theater with an audience.
”I had originally not wanted to see [Galaxy Quest] because I heard that it was making fun of Star Trek and then Jonathan Frakes rang me up and said ‘You must not miss this movie! See it on a Saturday night in a full theatre.’ And I did and of course I found it was brilliant. Brilliant.
”No one laughed louder or longer in the cinema than I did, but the idea that the ship was saved and all of our heroes in that movie were saved simply by the fact that there were fans who did understand the scientific principles on which the ship worked was absolutely wonderful. And it was both funny and also touching in that it paid tribute to the dedication of these fans.”
I posted it in another reply to you just below. He’s never been on video saying exactly what you said but he’s been quoted in articles/newspaper interviews. Snopes has a good summary with links to the publications.