In MTDVAT, you cannot remove the client. Instead, you can use the suspend option to suspend the user/Client, which prevents them from using MTDVAT services.. 

Follow the below steps on how to suspend the account of an client/user.

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.

PS:The clients account will be suspended and you can reactivate the account whenever you wish by following the same steps above..