Embarrassingly i have downloaded this and reading the first part - step 1a, i have come to a stop!

STEP 1a says - In your custom template son your cart, edit the tpl_header.php file and look for this line.
<?php if (($_SESSION['customer_id']) { ?>

The bold bit does not make sense, but i looked in the includes/templates/my_template/common/tpl_header.php but cannot find any reference to that code.

I have installed add ons before, which is why it's embarrassing.

Can anyone help me past step 1a?

Tia

Paul