Look at this guide for help to make a chat system (TwiceOnce has an idea too, dang I was too late)
Guide to the Ultimate Chat System
(wait, I just skimmed through this guide and the pictures are gone…)
Also, can you answer this question so I can help you a bit more?
EDIT: To add to TwiceOnce’s post, the devices you will need is probably a game overlay (to show the button to the chat), notification devices(to notify players once you chat), and popups(for the things you want to say in the chat).