The date picker is the small monthly calendar, just above the list of calendars in the control panel.There is also a pop-up date picker in the top bar of your calendar. Both work in the same way: use the arrows to move between months, and click the date within the month.
You can also use your mouse wheel or trackpad to navigate between months with both date pickers. Simply hover over the date picker, then scroll your mouse wheel or swipe on your track pad to move between months.
Scroll fast to move quickly or scroll or swipe slowly to move one month at a time. Once you’re at the desired month, click on a date and your calendar will update to your date selection.