Help with notifications reciever

Hello adalo fam. I am having a little issue with setting up my notifications. currently I am trying to find a way to to have the application send a notification to receiver when they have sent a message. i do have a receiving user option in my messages collection, but i am unsure of how to connect it to the icon so that when a message is sent the user recieving the message will be notified. any suggestions on how one might tackle this issue?