If you have recently inserted a topic in a group, you can use 'undo'; it will reverse the last change (ignore, merge, etc) that you did and you can apply it several times to reverse several steps. If you need to remove a topic from a group, and 'undo' is not a good option there is another way, and it is easy to perform if you follow these steps:
- Create a new group.
- Click the 'merge' icon
- Now click the 'drop' icon on the newly created group:
- Your topic will now drop into the newly created group and leave the former group.
- Click explore. Once the exploration is finished your topic will be outside the group.