Here's how to view the history of a Skill, and undo changes to it:
Using the left side navigation menu, scroll to your organisation's name, then hit 'Skills'
You'll see a list of all the Skills in use across your organisation
Find the Skill you want to view the history for and click the ellipsis '...' menu
Click 'View'
The Skill will expand β click the ellipsis '...' menu and click 'History'
Yo'll see the history of the Skill in the right side navigation menu. You'll be able to undo changes as required from here too.