@Anonymous User
Welcome to the forum. Yep, if the pass you want to watch is on your account and not theirs then you will have to log into their box and if you watch on there it will be added to your device list (so you would need to have a device slot free and be able to add a new device this month). If you wish to do this then open up the NOW TV app on their box and go to the My Account screen where you can sign out of their account and log into yours. Remember to sign out again afterwards.
Also remember that adding your friends box to your device list may mean you can't add another new device to your list until September - check your My Account > Manage Devices page to see if this is the case.
https://account.nowtv.com/device-management
