It's important that the date and time are correct as some phone functions won't work. In most cases, date and time are set automatically but alternatively you can set them manually.
Just so you know...
Please select the red text to see instructional images.
Find "Date & Time"
Press Date & Time.
Turn on automatic time zone, date and time update
Press the indicator next to "Set Automatically" until the function is turned on.
If you want to set the time zone, date and time manually, you need to turn off automatic time zone, date and time update and press Time Zone and the date. Follow the instructions on the display to set the time zone, date and time manually.