The watch is black and sometimes the icon appear but nothing else. When I touch it seems to work but again black?

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