You can set the Automatic Showing Approval by going to your specific listing.

Listings Tab > Select Listing address > Click Edit Listing Preferences 

Scroll down to "Auto Approve Showing Requests" make sure it is turned ON. By default, this option is turned OFF and requests are sent to the listing agent for approval. 

Click SAVE & UPDATE at the bottom of the page. 

NOTE: For all changes made, please remember to click SAVE & UPDATE which is found on the bottom part of the page to ensure your changes are applied.