Question about Beurer LB 55

You mean add it so that it smells delicious? Well, we didn't add any oils to ours, so there's a risk that the material of the vaporiser will discolour or rub off, but hey, why not? There is officially no way to add anything to it (neither a felt pad, nor a kind of "Chächeli" for it). My opinion: at your own risk. I'd rather leave it alone.