Overwrite Format (Single Event Format)

I’m having some issues overwriting formats. I want to overwrite the Single Event Format. I have the single_event_format.php located inside my theme folder:

theme/plugins/events-manager/formats/single_event_format.php

I just have <h1>Test</h1> within the single_event_format.php file.

I have this function in the functions.php file:

function em_custom_formats( $array ) {
  $formats = array( 'single_event_format' );
	return $array + $formats;
}
add_filter( 'em_formats_filter', 'em_custom_formats', 1, 1 );

I followed the readme.txt in the formats directory, not sure where I’m going wrong. Any help would be appreciated.

Thanks.