which is the safest way to remove all the personal information from samsung galaxy gear?

In order to delete all of your personal information from your Samsung Galaxy Gear (the mobile device is not affected), from the Clock screen, swipe to the right to access Settings  > Reset Gear  . Touch Reset to confirm and begin the reset procedure.

The process may take a few minutes while your personal data is removed and the device is restored to the factory defaults. Once completed, the device will return to the connection setup screen, and you will then need to pair it with your mobile device.

IMPORTANT : Your personal information cannot be recovered after using this feature.