The forum is how you report problems, request assistance, etc.
FYI, there is an existing thread regarding Netflix: Discover not showing any Netflix sources
You can mention Snowpiercer on that thread if desired.
Include the link to the movie from watch.plex.tv (Snowpiercer (2013) - Watch the movie free - Plex). It isn’t required, but it helps the Plex team that works on such issues.