You must be an administrator of the group to delete a sub-topic. In single-chats you automatically are an administrator and therefore can delete sub-topics. To delete 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 “Delete sub-topic”.
- Confirm with “YES”
Alternative: Go to the information of a sub-topic by tapping on the name of it. Then, scroll down. There you will find the button “Delete sub-topic”.