i found a apple watch but it is locked. how can i unlock for activation

You can't and you shouldn't even want to use someone else's watch. The watch is activation locked, which ONLY the real owner of the watch can remove. Turn the watch over to the authorities and don't expect anyone, including Apple to offer any help in giving you access to someone else's watch.

You can't use it. Post notices around where you found it, or take it to the police station, or if applicable, the Lost & Found department of the facility involved.

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