Once you add Bookmark(s) to an audio clip, you may want to edit or remove the Bookmark altogether. In PowerPoint you can’t edit a Bookmark — for example, you cannot change the time position of your Bookmark from 30 seconds to 28 seconds. To achieve this change, you have to delete the earlier Bookmark, and then add a new Bookmark on the time position that you want.
Learn to remove bookmarks from audio clips in PowerPoint 2013 for Windows.

