I am getting an error message: NO SIGNAL CHECK EXTERNAL INPUT OR SELECT ANOTHER INPUT USING INPUT BUTTONS, but I don’t know how to do this

I have received my Fibre phone adapter and change-over date but need a visit from a Technician to help me set it up. My phone is compatible but is situated in the hall and my VM hub is in the lounge. At 80 years of age I am not sure how my hub is con...