Edit default form fields

add_filter( 'rwmb_profile_login_fields', 'your_prefix_rwmb_profile_login_fields' );
function your_prefix_rwmb_profile_login_fields(){
    return [
                'username' => [
                    'name'     => __( 'Username or Email Address', 'mb-user-profile' ),
                    'placeholder' => __( 'Username or Email Address', 'mb-user-profile' ),
                    'id'       => 'user_login',
                    'type'     => 'text',
                    'required' => true,
                ],
                'password' => [
                    'name'     => __( 'Password', 'mb-user-profile' ),
                    'id'       => 'user_pass',
                    'type'     => 'password',
                    'required' => true,
                ],
                'remember' => [
                    'desc' => __( 'Remember Me', 'mb-user-profile' ),
                    'id'   => 'remember',
                    'type' => 'checkbox',
                ],
                'submit' => [
                    'std'        => __( 'Log In', 'mb-user-profile' ),
                    'id'         => 'submit',
                    'type'       => 'button',
                    'attributes' => [
                        'type'  => 'submit',
                        'name'  => 'rwmb_profile_submit_login',
                        'value' => 1,
                    ],
                ],
                'lost_password' => [
                    'type' => 'custom_html',
                    'std'  => '<a href="' . esc_url( add_query_arg( 'lost-password', 'true' ) ) . '">' . __( 'Lost Password?', 'mb-user-profile' ) . '</a>',
                ],
            ];
}