Make sure you have a backup ready before you follow these steps

Passcodes can be tricky to remember, so it’s no surprise if you’ve forgotten your Apple Watch passcode – or, you simply want to remove it.

Apple requires you to set a passcode if you opt to use Apple Pay on the smartwatch, though you can, of course, remove it if you don’t mind foregoing the feature. And, as we say, in the unfortunate event of your passcode slipping from your memory, it’s possible to still recover.
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Read full post here:
https://www.wareable.com/apple/how-to-remove-apple-watch-passcode-forgot-reset-7233