How to get the free 3 months added to my existing subscription?

I for many years have subscribed to many of your applications and in the most cases very happy with the results. HOWEVER,as a reward for being a loyal customer, you now offer a free 3 months to a number of applications to which I already subscribe. How can I get these 3 months added to my existing subscriptions, as your web site is not set up for these type of situations?