Hello,
Disconnect the battery to let the back up power drain, (around two
minutes )
DO NOT SHORT the positive and the negative  battery terminal together
to accelerate  the drain of the back up power
The back up power is inside the air bag diagnosis module  and is not
serviceable

Do not hammer  the steering column used a puller to remove the steering
.(just in case you have a collapsible steering shaft.

Denis
Quebec Canada

Westie 85