If you’d like to change the first day of the week that displays on your calendar views, you can easily do this right from your global WordPress settings.
1) Navigate to Settings > General from your WordPress sidebar. You’ll find the drop-down menu selector for Week Starts On near the bottom of this settings page.
2) Select your preferred day from the drop-down menu provided, then click the Save Changes button to apply your changes.
Your selection will automatically be applied to your calendar views and can be changed at any time.