With this, they're referring to the nozzle of the bidet attachment that would rest at the back of everything. If it gets soiled, you can press that button and avoid sticking your hand into the unit.
I actually didn't know what "WAND CLEAN" meant (I was thinking something with genitalia) until your translation, so you actually helped me. Thanks! I was just expanding on it a bit for people who might still be lost :)
Come on in ladies.