how do you rejoin a group message

If you can't add or remove someone in a group message

• You can only remove someone if the group has four or more people, and everyone is using an Apple device, like an iPhone or iPad.
• You can only add someone to a group message if they're using an Apple device. If you want to add someone to a group message but they're using a non-Apple device, you need to create a new group message. That message will use SMS/MMS by default since someone is using a non-Apple device.
• You can only add someone to a group message that already includes three or more people. You can't add someone to a messages conversation that you're already having with just one other person.