Unfortunately, if you signed up for an account directly through your Apple Device or Roku and did not provide Motor Trend OnDemand (MTOD) with your email address (the email address associated with your Apple or Roku account is not shared with us due to privacy reasons) you will not be able to watch MTOD on any other device.
Additionally, MTOD customer support will be unable to assist you as we will not have any internal records of your account. Your account information is stored within the device you subscribed on. There is no way possible to connect our system to your device after the fact.
In order to remedy this situation the only option is to cancel your current subscription, and then re-sign up entering your email address or through a desktop/laptop computer. Unfortunately, since MTOD does not have any record of your initial transaction there will be no possibility of refunds or credits due to this issue.