reset my activation lock passcode

It would seem you may be speaking about your Apple ID password, since that is what enables/disables Activation Lock. See this if you have forgotten your Apple ID password and you need to recover/reset it. If you forgot your Apple ID password - Apple Support

If you're talking about the passcode to unlock your screen, see this guide:--> If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

If you meant something different, please explain. Thanks

Regards

Giulio