Change mobile data usage warning & billing cycle date - Android

How to change mobile data billing cycle start date and data usage warning on Android phone ? I can see item "Billing cycle and data warning" in the settings, but it is disabled.

To change the billing cycle start date or mobile data usage warning on Android, you have to first enable mobile data in quick settings menu (swipe from the top of your screen to the bottom) or go to:

Settings > Connections > Data usage > Mobile data

Then you can change the billing cycle and data usage warning limit in:

Settings > Connections > Data usage > Billing cycle and data warning > Start billing cycle on

Settings > Connections > Data usage > Billing cycle and data warning > Data warning