How to send a text every time you open TikTok

So I have been seeing all over TikTok people posting this kind of videos where they open this specific app like Instagram, Wattpad , Twitter you get the drill and it send a message to one of their friends , I wanna do that but idk how to do it or if it’s possible to🐈✨💕 If someone can help pls do🛐🛐tyy