You can find the Add Members setting in a group’s conversation settings page.

To add a colleague to an existing conversation:

  1. Navigate to the conversation you wish to add members to
  2. Click the group name at the top of the screen (if the group does not have a name, the group name will be the members in the group)
  3. Tap Add Members
  4. Search for the desired members, and tap on them
  5. Tap "Done"

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