Hi
Apple does not offer a screen repair or screen replacement service for Apple Watch. Your watch will instead need to be replaced.
The AppleCare+ service fee / excess varies by country and by Apple Watch model.
In the US, for example, it is currently $69 plus applicable tax for Apple Watch models except Edition and Hermès:
AppleCare+ - Apple Watch - Apple
Contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider to arrange for your Apple Watch to arrange service and confirm the applicable cost: