so i already looked over this thread: 

https://stackoverflow.com/questions/63557264/odoo-13-how-to-use-message-post-to-send-message-in-the-chatter/76754252?noredirect=1#comment135317243_76754252

but i am still lost on how i should proceed with creating the event, i am fairly new to odoo so i would appreciate any help.

I tried adding a new button in the composer tool bar, that worked as expected however said button can't use the message_post() method of the channel model cause it counts under the composer model.

Edit: sorry about the mix-up i meant to say i need to add an additional button in the discuss tab where while talking with someone in a chat or a channel i can ping them to give them with a predetermined message in the code.