combination low res HDMI & Tinkerboard

Hi there just starting my project for a mediaplayer for my youngest son, and chose volumio with an Asus tinkerboard.
Installation succeeded, as well as the installation of the hdmi display, problem is im unable to start it with a lower resolution.
Some manuals refer to changing the config.txt, but there’s no config.txt in the boot folder.
The full HD resolution is really bad on a 5" screen, so i want to lower it.
next step will be trying to get the touch to work, but without a proper resolution it would be pretty pointless.
anyone with an idea how to get the tinkerboard to start in the native resolution of the screen?