Once an authorisation has been issued, it shall remain in effect for a period of 18 months. The authorisation can't be revoked, instead you can "suspend" the account.

RoadMap to Suspend your Account:  

 RoadMap:  Hamburger menu → Client/Trader Manager → Select the client to whom you wish to suspend and click on View/Edit → Manage Assistant Administrator
→  Now, click on the  manager user option of the same client you wish to suspend → Suspend Account →  Enter the passcode with reason on why you choose to suspend the account  →  Click Confirm.