Be warned - lots of unofficial facebook groups and WhatsApp/messenger groupchats aren’t run by universities or even students. They’re used by event organisers to use reps to promote freshers events (unofficial ones, tickets sold through fatsoma). The reps are pretty stupid and repetitive and just bang on about freshers events and ticket links and drinking all the time.
The key is to use these groups to find actual genuine freshers by asking people what they are going to study, where they will be living etc and then connecting with the real freshers on other platforms.
This is one benefit of TSR - the fake freshers can’t get a foothold here so when you do find someone from your university or course or hall they are likely to be real!