HOW TO REPAIR apple watch black screen with a single orizontal line
the only think on te watch is one horizontal linea on the top of the black screen
Apple Watch Series 4, watchOS 9
As per Apple if Apple watch screen damaged then you have to replaced the watch with new one or display replacement if available in your country or state so please visit your nearest AASP or Service & Support. Apple Store.
I want to tell you one more thing if you send any picture of your damaged product.
or else your device is damaged due to single line crack then Apple can change your watch or display without any charge.