I forgot my iCloud password what should I do?

Reset Apple ID password If you forgot your Apple ID password - Apple Support

Not necessary you always need account recovery from server , its not necessarily you might be using 2FA account , the Apple ID should be signed in the device ( essential ) .

1. Apple ID account recovery - How to use account recovery when you can’t reset your Apple ID password - Apple Support
2. Contact Apple ID support - Apple ID - Official Apple Support