You must be an administrator of the group to rename a sub-topic. In single-chats you automatically are an administrator and therefore can rename sub-topics. To rename a sub-topic proceed as follows:
- Go to the main-screen.
- Look for the respective chat (single- or group chat) that you want to edit.
- Tap and hold the chat until a context menu opens.
- Choose “Rename sub-topic”
- Now you can enter the new name of the sub-topic and confirm it with “Continue”
Alternative: Go to the information of a sub-topic by tapping on the name of it. With the help of the Pen-Symbol you can also change the current name.