yvonne yu: You can change the default Experience Service URL from your ThingWorx Studio Homepage as shown below:
Edit or select the default ES URL and click Done.
Note: The auto-configuration functionality in Studio only applies to Studio Trial Users, not for commercial customers.
Since you are using Commercial instance you should have received a zip file with all their ThingMarks from PTC Cloud Service team. Please check the attachments from the initial email sent from PTC for more detail.