Re: "The watch is black, sometimes the icon appear but again it goes black, what should I do?
If the watch is just 4 month old"
Seems with a watch that new, it may be best to check with the experts:
There are a few different support options listed below that you may want to consider:
How to find the serial number or IMEI for your Apple Watch - Apple Support
Where to enter the serial number to see what options are available to you: (you may see online instructions)
Check Your Service and Support Coverage - Apple Support
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Else: One stop for technical support, Apple hardware service, and software support.
Call Apple Support at 1-800-APLCARE (or use the app)
AppleCare Products - Apple
or
If you decide to visit a nearby Apple Store: a Genius Bar reservation is recommended:
Genius Bar Reservation and Apple Support Options - Apple
Also: See a list of Apple phone numbers around the world
Contact Apple for support and service - Apple Support