There is nothing in the $_POST["formSubmit"]. Assuming the first page is called "sendfrom.php", then change header in the "myfile.php" as follows:
1. The static way:
header("Location: sendfrom.php");
Or,
2. The dynamic way:
header("Location: ".htmlentities($_SERVER['HTTP_REFERER']));
Looking at the added code, another problem surfaces => echo cannot come before header. Check this out.
example