If you've beat all the computer personalities and want to start over, or want to clear your progress for any reason, you can reset your crowns in your settings!

Simply go into your settings by clicking on the settings gear icon in the bottom left of any page on Chess.com, then click on 'computer' in the left menu.

Then, click on the Reset Crowns button, and click Yes

All your crowns will be removed, and you'll have a fresh start with the computer: