Date and time are automatically set from your phone but can be set manually if, e.g., your smartwatch isn't connected to your phone.
Slide your finger upwards starting from the bottom of the screen.
Press the settings icon.
Press Date and time.
Press Set date.
Slide your finger up or down on the screen to set the required date.
Press Set time.
Slide your finger up or down on the screen to set the required time.
Press Select time zone.
Press the required time zone.
Press the Home key to return to the home screen.