Edit the EVENT Form in SharePoint

Our SharePoint Home site/page (/home) has the built-in Events element

When you click 'Add Event', you're taken to a new Form, which has a 'Category' field.  I've added a new field (Subcategory) to the List, but it does not appear on the Form.  Is there a way for this to appear when a user adds a new Event (the Category and Subcategory should also be visible when people view the Events calendar).

I've tried going into the Settings for this List Item, but there's no way to edit the form.

Can anyone advise if this is possible?

Thanks

Brian