Here is the code I have tried entered correctly.
add_action( 'acf/save_post',
'my_acf_save_post', 10 );
function my_acf_save_post( $post_id ) {
// Get value of field 1
$value1 = get_field( 'pds_project_manager',$post_id );
// Get value of field 2
$value2 = get_field( 'architect', $post_id );
update_field( 'project_user_email_select', $value1 . $value2, $post_id );
}