If the freezer is still off - you could get a hotplate and boil some water in a low pot, mixed with a good amount of the baking soda. You could also put some liquid freshener in it (febreze) which can help neutralize.
Remember that if the freezer is plastic lined - the odour has actually permeated the plastic and not just the surface, so it will need to be warmed up to effect sufficient neutralization.
The same goes for a microwave oven for instance: How many times have we all burned popcorn in the bag - and the burnt odour lasts for weeks unless neutralized somehow. Quite a nightmare but it can be neutralized in this manner.
Be careful and monitor the "boil" - you don't want anything to melt, and keep the towels handy to mop up the moisture/condensation.