assigning keyboard shortcut to button in app

MacOS High Sierra (old hardware), BTT 2.340. I have a simple app, the UI consists of a few buttons. Picture a TV remote control. Some of the buttons have keyboard shortcuts, some don't. Those that don't, I'd like to assign keyboard shortcuts. They have no menu selection to assign from system preferences. Is there a way to do this in BTT? I've given it my best shot trying to learn how.