Change Ultimate Member text/label with the filter hook

um-core-fields.php

<?php
/*
* title & label Gender to Gender Identity
* see: https://github.com/ultimatemember/ultimatemember/blob/master/includes/core/class-builtin.php#L832
*
* @param 'title', 'metakey', 'type', 'label', 'required', 'public', 'editable', 'options'
*
* @return array
*/
add_filter( 'um_core_fields_hook', 'um_custom_modify_text', 10, 1 );

function um_custom_modify_text( $core_fields ){
    $core_fields['gender']['title']      => __( 'Gender Identity','ultimate-member' );
    $core_fields['gender']['label']      => __( 'Gender Identity','ultimate-member' );

    return $core_fields;
}