You could navigate to Designer Studio and under the Designer Studio > Application > Recent Actions menu you could see all the rules you modified and retrace your steps to either undo or delete the rules. 

The other option you have is to have your exercise system reset.  You can do this yourself on the Course Overview page by clicking the Options button and selecting Reset Exercise System or you can email your request to SelfStudySupport@pega.com. Please make sure to include the course and version you are currently enrolled in to make sure we reset the correct exercise system.

Please let me know if this resolves your issue,

Sean

Pega Academy Self-Study Support Team