A conversation block is a group of questions and messages. These blocks are indicated beneath timeline points (seen the images below as grey, blue and pink circles). By hovering over the timeline point is possible to make actions based on the conversation block beneath it.

If you wish to delete a conversation block, after hovering over a timeline point, click the delete action (bin shaped) icon.

To confirm deleting this conversation block click the pink 'Yes, delete' button that appears on screen (seen in the image below), this will completely remove the conversation block from the timeline. Alternatively, click 'Cancel' to keep the conversation block. 

Note: it is not possible to delete a conversation block if your conversation has already been published and has the label of 'Active'.