since i bought this one from blackmarket or I think it was stolen before . How can I set it up?
You cannot, recycle the Apple Watch.
If you can't get in touch with the seller, you can't use the Apple Watch.
Each Apple device is linked/associated with an Apple ID of the person who did the setup.
Activation Lock prevents anyone who is not the owner from using this Apple Watch.
To unlock the Apple Watch, you need the Apple ID and password of the previous owner, that were used during set up.
So you have to contact the previous owner.
The previous owner has to read -> this Apple article: What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else
What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support (IE)
Then the previous owner has to remove the Apple Watch from his account, see this Apple article:
Check your Apple ID device list to see where you're signed in
Check your Apple ID device list to find where you're signed in - Apple Support
Then you can sign in with your own Apple ID.
See the following Apple articles:
About Activation Lock on your Apple Watch
About Activation Lock on your Apple Watch - Apple Support
How to remove Activation Lock -> How to remove Activation Lock – Apple Support (UK)
Read this before you buy a 2nd hand device (this warning also applies to purchasing a 2nd hand Apple Watch).
You can also contact Apple support for help, -> Get Support (apple.com)
You have to show proof of ownership of your product, provide all documentation showing your purchase of the device.
If you do not have additional proof of ownership, contact the reseller. They may be able to provide the original purchase document.
Once Apple receive your proof of ownership, Apple will further review your request and provide an update.
See also -> Keep your receipt after you buy an Apple device
Keep your receipt after you buy an Apple device – Apple Support (UK)