Click on hamburger menu located on the right-hand side of the top-right-hand bar of your MTDVAT app. In the menu bar, you will see the option “Client Manager (view/edit)”.

 Here, you can edit the required information and save it in the same page.

RoadMap on how to edit contact details of  System Administrator: 

RoadMap: Hamburger menu → Client/Trader Manager → Select the trader to whom you wish to edit the contact details and click on View/Edit → Company/Agent Setup → 
→Manage Assistant Administrator → Click on blue button → view / edit details →Click Save data & back.

Pls view the video demo below how to add & view edit assistant user details.