The cable adjuster is under the handbrake lever, if you pull the lever up you can see it in the gap under the lever, you'll need a 10mm socket and a long reach bar to get to it.
Not too up on old Nissans but maybe if self adjusting drums are used, they are not adjusting. They used to get crudded up. Always manually adjusted mine on the Fords.
Adjusting brakes will then have an effect on the handbrake.