You can add any shot plan to the calendar as follows.
First, set up the shot plan as desired: set the pin position(s), date and time for your planned shot. When ready, tap Share/Action:
In the bottom row of the Share sheet, swipe left to show more options if necessary:
Choose Add to Calendar:
You’ll need to allow TPE to access your Calendar in order to add an event to it:
A new event is displayed. You can edit the title, choose which calendar it should be added to (if you have multiple calendars configured), and set reminders. The shot includes a short link which will open TPE and display the planned shot as you had it configured. Choose Add to save the event:
The added event will then be visible in your calendar: