This was a year ago, I can't find the video I used, it was also max 5-10 seconds. I remember I did the video by recording powerpoint slides, so I used phone or screen recording to record and then each slide of the powerpoint would move to the next one when I clicked or wanted animations. The powerpoint slides had pictures and texts. It was very amateur.

This was the app, I'm in Canada: https://itunes.apple.com/ca/app/lucid-see-who-likes-you/id12...

I contacted them through Instagram and explained my app and asked if they wanted to post the video for me. Some said yes. Some didn't. I think I also framed it as marketing experience for them too but I'm not too sure what I said exactly, I didn't really have any money at the time. Also some were friends of friends of friends and it wasn't as strange in asking them to post but I still didn't know these people.

I'm not as focussed on the app anymore and sometimes maintain it, I keep it more as a side project link for my resume.

Overall, you just need to be brave enough to message them, I was a bit shy and unsure at first and then afterwards I got used to it because it's easier to communicate online and it was the cheapest alternative I could think of.