Featured image appearing twice in event page

The featured image at the top is inserted by your theme. You can remove this using the following css:

.event-template-default .big-preview {
    display: none;
}

Where do I insert this?

You can add it with Quick CSS it in the Enfold Theme:

The Quick CSS section is provided in the theme options to add your custom CSS code easily and quickly. You can access this section from the Enfold theme Options > General Styling > Quick CSS

See the documentation here: https://kriesi.at/documentation/enfold/add-custom-css/#quick-css

joneiseman, your expert support of this plugin is incredible! Are you paid Events Manager staff?

No, I am not part of the Events Manager staff.