Hi,
thanks for help. Although it's now a long time since I originally asked a question, I needed this again and I decided to write here my solution for anyone that would be in same dilemma. The answer was is almost correct and it pointed me in the right direction.
I forgot to answer it last year, because I solved this some other way and I totally forgot about this question.
Because I was using [mb_user_profile_info id="rwmb-user-info"]
shortcode, I needed to create a filter like this:
add_filter( 'rwmb_profile_info_fields', function( $fields ) {
error_log(print_r($fields, true));
$fields['password']['attributes'] = [
'title' => 'Username required text'
];
$fields['password2']['attributes'] = [
'title' => 'Password required text'
];
return $fields;
});