I cannot seem to be able to program these buttons.
Hi Brian Bycroft, before you can program your tablet's press key buttons, please make sure to install the tablet driver. You can download the latest version from this link: Huion H420 Graphic Tablet Drivers. Please check these articles to guide you on how to properly install it:
NOTE: Do not connect your tablet to your computer as you install the driver.
After installing the driver, please connect your tablet to your computer and make sure that the driver shows "Device is connected" as shown below:
Click on "Advanced Setting" then click on the button you want to set then choose which function you want it to perform.
HUION Customer Support