I think it is to do with buttons on the electricity meter, but it is better to get the installer back to finish the job they should have done for you. There are too many rushed and incomplete installations and the installers need to be held responsible.
I'm having the same issue and my IHD is just in demo mode I cant see any option to pair it or set anything up.
Did you find out what needed doing? Did I need to get the engineer back?