Does his phone have a wifi hotspot? He could connect to that to access the internet and set up his Express. Once at the Roku home screen, Roku menu path Settings / System / About will show him the MAC address among other things.
Once his base wifi is set up he can reconfigure his Roku to connect to the base system.
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I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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