This article explains how to change the date and time on macOS Catalina (10.15) through macOS Sierra (10.12).
When you first start up your Mac, macOS will prompt you to select your time zone. It will then automatically set the date and time based on this setting. If you’re traveling or want to display a different time zone for work, you can manually change the date and time on your Mac.
To change the date or time on your Mac desktop or laptop, follow these steps.
Select the time indicator on the right side of the menu bar to open a dropdown menu. Then click Open Date & Time Preferences.