Reset Achievements on Steam
To reset achievements for a game on Steam, follow these steps: 1
- Run steam://open/console in a web browser.
 - Open the new Console tab in the Steam client.
                    Then...
                    
- Reset one achievement:
                    
achievement_clear <application ID> <achievement name> - Reset all achievements:
                    
reset_all_stats <application ID> 
 - Reset one achievement: