Blogs Mu - Join our community now button

I may have not installed this correctly to work the way it is supposed to. I have multisite and my primary domain is not the area where I installed this theme. So as an example lets say my primary domains is john.com and I installed this on bill.com. When I hit the "join our community now" button it goes to John.com even though it was installed on bill.com. So I need to know where can I change the link so it goes to some other location. I am very new to this but I learn quick. It appears that this button should go to a sign in screen or something. All help appreciated.