gistfile1.php

// Add your own function to filter the fields
add_filter( 'resume_manager_resume_fields', 'custom_resume_manager_resume_fields' );

// This is your function which takes the fields, modifies them, and returns them
function custom_resume_manager_resume_fields( $fields ) {

    // Here we target one of the job fields (location) and change it's placeholder
    $fields['_candidate_location']['placeholder'] = "Custom placeholder";

    // And return the modified fields
    return $fields;
}