Top two rows of my iPhone are not working after screen replacement

This is unfortunately a fault that can only be solved by replacing the LCD/digitiser assembly again.

It may just be a faulty part (I find them very hit and miss) or it could be that the flex got bent/crimped during installation. They are very fragile and don't take a lot to damage.

It might be worth removing the screen again to disconnect and reconnect the digitiser zif connector in case there's something wrong with the contact between plug and port.

Personally though I think it sounds more like a digitiser fault