Discover Magazine login

I subscribed to the Discover Magazine with my iPad 2 since October 2013, and have been comfortably purchasing and having my magazines year after year without hassle. A recent app development made my iPad 2 unable to run the magazine’s app. I had to acquire a higher iPad version. So I got an iPad 6. After transferring the magazine’s app to my new iPad, I am faced with a login interface that is demanding a login identity and password that I don’t seem to be aware of. I can see my monthly subscriptions loading alright but I can’t access them because I am unable to get pass the login interface. I simply can’t remember having the required information for the interface. My Apple ID and password aren’t working. There is no “Forgotten login info” link for possible resetting. I have a whole year’s subscriptions. How do l go about this problem please. Where and how can I get the required information or reset it?