How do you go about adding or removing elements from the add event modal. I need to add a select box and a radio button.

getElementsByName method returns NodeList of all elements with name="description" set. You can find more information about this method here.

I prepare a snippet for you where you can see 2 examples of how to get input value with name="description": https://mdbootstrap.com/snippets/standard/grzegorz-bujanski/4506347#js-tab-view

After clicking the Add button in the modal, the event addEvent.mdb.calendar is triggered. You can listen to this event and use it to get all event data and save them on your server.

calendarElement.addEventListener('addEvent.mdb.calendar', (e) => {
  // all event data is returned as e.event.  
  // you need send this data to your API. ForExample:

   fetch('https://your.api/new-calendar-event', {
     method: 'post',
     body: JSON.stringify({
       summary: e.event.summary,
       description: e.event.description,
       startDate: e.event.start.date,
       startDateTime: e.event.start.dateTime,
       endDate: e.event.end.date,
       endDateTime: e.event.end.dateTime,
       colorBackground: e.color.background,
       colorForefground: e.color.foreground
     })
   });
});