Alexa 'offline' on Amazon fire hd tablet

[robbocop33]

Hi, i personally have an amazon fire hd which i bought new a few days ago, Alexa worked great straight away. However, an elderly friend of mine bought an identical model of fire hd 'used' and his Alexa is permanently offline?
What i've noticed is previous owner's echo dot etc are all showing up under registered devices, will i need to scrub all this and start a new account for him through Amazon? Does his fire hd have to be known through an Amazon account for Alexa to function? Thanks.