Log in to your account at training.mulesoft.com. Click on Dashboard from the top menu.
Under Enrollments, click into Certification Exams. Locate the exam you would like to reschedule.
To Reschedule your exam, click the BLUE calendar icon next to the name of the exam, and select a new date and time. 
If you need to cancel your scheduled exam, locate the exam you would like to cancel, then click the RED calendar icon with an “x” inside of it, next to the name of the exam. You can come back to Reschedule your exam at a later time.
If you are registered at a Webassessor Test Center and need to make any changes to your scheduled exam, please log in to your Webassessor account and click the Reschedule or Cancellation button next to your scheduled exam. There may be a reschedule or cancellation fee applied if you are trying to reschedule your exam within 72 hours of your scheduled start time. More information can be found here.