Event Calendar – index related venue

<?php

// Add to functions.php
// Change "YOUR_FACET_NAME_HERE" to the actual facet name (not label)
// Set your facet's data source to "_EventVenueID"

add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'YOUR_FACET_NAME_HERE' == $params['facet_name'] ) {
        $venue_id = (int) $params['facet_value']; // the venue's post ID can remain the slug
        $params['facet_display_value'] = get_title( $venue_id ); // set the venue title as the label
    }
    return $params;
}, 10, 2 );