APP: Press the three lines on the top left-hand corner of your screen. Tap the "My Additional Users" option. You can view your current users here. At the bottom of the page will be an "Add New Additional User" tab, press this and input all the relevant details and press add.
WEB: The Additional User tab can be found on the left-hand side of your screen. You can view your current users here. You can also add any additional users by clicking the Add New Additional User tab on the top right of your screen.