As the creator of a group conversation using a Pro account you are able to delete this group. This will delete all content for all participants of the group on all devices.

There is no option to restore the content. The participants will be notified about the group deletion.

On desktop:

In the conversation list:

1. Click the group conversation.
2. Click the group name at the top of the screen.
3. Click Delete group.
4. Click DELETE.

On mobile:

In the conversation list:

1. Tap the name of the group you want to the add the service to.
2. Tap the group name at the top.
3. Tap   at the bottom right corner. 
4. Tap Delete group.
5. Tap Delete.