[EDITED]
Never mind, worked it out. This thread can be closed.
Go to the Xbox store on the halo 5 guardians page in the add ons it will be there and you can download it for free.
Locking at OP’s request 
[EDITED]
Never mind, worked it out. This thread can be closed.
Go to the Xbox store on the halo 5 guardians page in the add ons it will be there and you can download it for free.
Locking at OP’s request