Hi9 Pro won't connect to mobile network

My Hi9 Pro screen got broken. Got a new screen from Chuwi. Fitted the new screen and touch didn’t work. Chuwi sent links for flashing the firmware. Eventually one worked and touch is good. Now it won’t (or can’t) connect to mobile network anymore.
Does not show any bars. Says "No Service)
Is it possible that the new firmware changed the frequencies?
Is it possible to change them back by entering “Engineer mode” like some other phones?
This device had American ? Australian frequencies and worked well before the screen change.