You need to log-in through a web browser to add a bank account. You can't add one through the mobile app.
To add a bank account please follow these steps:
Click your name in the top right corner of the dashboard.
Click on Profile , then Banking and Finances from the menu.
Click on the large tab 'Add a bank account' , enter the details and select the option to upload your void cheque. Once you do that you hit the green Submit button.