ee_venues.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file
// change the post type slug URL to be "locations"
add_filter( 'FHEE__EE_Register_CPTs__register_CPT__rewrite', 'my_custom_venue_slug', 10, 2 );
function my_custom_venue_slug( $slug, $post_type ) {
    if ( $post_type == 'espresso_venues' ) {
        $custom_slug = array( 'slug' => 'locations' );
        return $custom_slug;
    }
    return $slug;
}