Evens Calendar - Month view default tooltip

functions.php

<?php


add_filter( 'tribe_events_template_data_array', 'rt_mt_month_view_default_image', 10, 3 );

function rt_mt_month_view_default_image( $json, $event, $additional ) {
    // if featured images is empty
    if ( empty( $json['imageTooltipSrc'] ) ) {
        $json['imageTooltipSrc'] = "YOUR_IMAGE_LINK";
    }
    return $json;
}