Apple Watch don’t pair

With no description of what you are seeing when it doesn't work all I can suggest is use the Apple support documents Set up your Apple Watch - Apple Support and If your Apple Watch isn't connected or paired with your iPhone - Apple Support as a guide, and post back with more details if you are still unable to get it working.

A red sign.... what kind of red sign? What does it look like? (Description or photo).

This sounds more like the watch is already paired, because an unpaired watch is pretty much brain dead and only knows how to display the initial setup screens illustrated in the support docs I linked above. It certainly doesn’t have a device name you would know about to enter it manually.