Ring doorbell wired impossible to reset when installing

Bought a second hand Ring video doorbell (latest model, not the Pro version). My electrician installed it. He id not connect it to the old/excisting chime, because I have a Ring chime that I want to use. He put in a transformer in the socket cabinet and connected the doorbell to this transformer. There is power into the doorbell, a solid blue light is there. But it is not responding when I try to reset it with the orange button (also tried holding the button for a long time to hard reset it). So it is impossible to get it into installation mode/white light flashing. Any hints?