When you purchase subscriptions through third parties, it isn't always possible to use that login on different devices. When you got it from the Apple store, it might only work on iOS devices. I don't know that for a fact for that particular subscription, but it does with some other providers.
When Disney+ is first installed, it doesn't have any user credentials. When you mention a comp subscription, it sounds like you had some sort of credentials entered. To get to the login, you must first log out of the current credentials. If you can get into the channel, there's a menu on the left side of the screen, and settings is at the very bottom. Under Settings is the option to log out of the existing account.
If you can't get into the channel any longer, then you need to uninstall the channel, reboot the Roku (do NOT skip that step), then install the channel again. You should then get to the new user page, which should allow logging in with new credentials.
Dan
Roku Community Streaming Expert
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