On the WF-3620, you can customize the buttons as you please with the help of the Epson Event Manager application. Epson even created a help page with instructions and images that show exactly what and how to configure the device as you please when you press one of the buttons.
Of course, this implies that you have the software installed, otherwise download or install it from the support disc that arrived with your device.
To download the software, access the official website and expand the Other software section.