Your unit should be the same as my TTN uno. Arduino and a RN2483. If you have setup your arduino IDE and have a working sketch for KPN i think you should only need to change the network and apps keys.
network key: mac set nwkskey 2B7E151628AED2A6ABF7158809CF4F3C\r\n
apps key: mac set appskey 2B7E151628AED2A6ABF7158809CF4F3C\r\n
Above lines should be in the sketch somewhere for the KPN network (with different keys off course;)
My setup is still inside the house so if it'll reach Sassenheim i don't know.