Scroll down to the page and you should see the “Custom Fields” box. See screenshot below
Now Click Select under “Name” and select event_date. Enter event date under value. Note: put zero for single dates, ex: 05
Now Click on “Add Custom Field” button, it may take a few seconds to add.
Now you have to do the same for Month. Use capital letter and three letter month abbreviations so that the format looks neat and consistent. Example: for January (JAN), February (FEB) and so on..
Now Publish or Update your post like you normally do.