To setup users additional access for an existing user such mobile app access, follow these steps:
Login to your CStore Essentials account.
On the top left next to your store name click on the Manage Account button. [?]
On the top right, click on Users button.
Find the user you wish to update and click on the details icon.
Click on the "+" button to assign other accesses or the Delete button to remove a particular access level.