Open up the group message. Hit the three dots at the top right hand corner. Then press and hold on add or remove people. You have to press and also hold. A list of the recipients will appear on top ...
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Open up the group message. Hit the three dots at the top right hand corner. Then press and hold on add or remove people. You have to press and also hold. A list of the recipients will appear on top with minuses next to their names for deleting. I had to go to this process twice, first deleting their names and then their telephone numbers, but I think that was a fluke. Should be able to do it in one step.