If you mean the usual months dropdown, then most likely the plugin might be disabling it via the following filter:
/**
* Filters whether to remove the 'Months' drop-down from the post list table.
*
* @since 4.2.0
*
* @param bool $disable Whether to disable the drop-down. Default false.
* @param string $post_type The post type.
*/
if ( apply_filters( 'disable_months_dropdown', false, $post_type ) ) {
return;
}
You could try to override it with:
add_filter( 'disable_months_dropdown', function( $disable, $post_type )
{
return 'event' === $post_type ? true :$disable;
}, 999, 2 );
where you might need to adjust the post type slug and priority to your needs.