I found an apple watch in the street there is some way to contact the owner or to be able to unblock it to use it

Greetings EmmanuelH28,

Thanks for coming to the Support Communities to report a found Apple Watch. That's wonderful. Your best option is to report the watch as found to the local authorities. According to Apple's Privacy Policy found at www.apple.com/privacy they wouldn't be able to help you in getting in contact with the owner. And if the owner files a police report as well, then the situation could be handled lawfully.