ages ago credit friends initial link login managed page pay paypal setting shop site type website

I set up a shop ages ago and when I use that and get to the initial paypal page where you can either login to pay or pay by credit card there is a link back to my site. I can't figure out how I managed to add this. I'm setting up a shop on my friends website and we want the same type of link back to his website.

Anyone know how to add this?