In order to review an internal comment’s revision history, you first have to reach the comment’s edit screen. You can achieve that in one of two ways:
- Finding the comment in the dedicated list view and clicking on the Edit action.
- Finding the comment inside the attached post’s metabox, then navigating to the comment’s actions and opening the Edit comment link in a new tab.
The revision history will be available inside a dedicated metabox on the newly reached edit screen: