The config files hold the device properties and the WiFi network information that the sketch uses to connect to WiFi.
Templates for the two required config files are available at arduino-via-hono/config_template/.
You should copy the config template files to your sketch folder (e.g. ditto-examples\arduino-via-hono\examples\opla_kit) and fill in the required properties.
You can copy most of the properties which need to be replaced, marked <in angle brackets>, from the provisioning.json file that was generated during the device provisioning step.
After that, you should change the file name extension from .h_template to just .h
This file will hold the credentials which allow the Arduino board to access your local WiFi network.
Make sure you keep the quotation marks for the strings.