Oh hi! Thank you! :) The knife and the Op are my favorite!
I don't actually know how we find people for these labs. I can ask how we do it. :)
I can! The very short answer is we use data analytics and surveys to identify groups of players we're interested in testing with, and then send out email invites to ask them to come playtest with us.
Obviously things are a bit different now with quarantine in the US, but we're still running tests, discussion groups, etc. with players in the same way, just remotely. If you're interested in this sort of thing, check the email you have associated with Valorant periodically - you may find a survey or email there that asks about your availability to playtest on a given date!