The widgets are part of the Notifications.
Drag down from the top of the phone. That shows you your notifications usually. If you closed notifications while on the widgets it will show you the widgets.
Swipe right to get to the widgets.
Scroll to the bottom to tap on the Edit button.
At the top are your current widgets, you can remove them by tapping on the red circle, then tap on the Remove button.
You can re-order them by pressing the three lines on the right and dragging them up and down.
Under that section are the widgets that are not being used.
You can add the widget by tapping the green circle, then move up as you want it.
I think you want the Up Next or the Calendar widgets on the top
Tap Done in the top left to see the widgets in action.