After all the fasteners are removed from inside the trunk, you should be able to pull or gently pry the taillight assembly away from the body from the outside. It may have a light coating of adhesive holding it in place. Once the assembly is removed, the bulbs should be accessible; either by removing the lens, or by going in through the back of the assembly. There might be one or two more fasteners which the service adviser did not mention. If there are more fasteners, they might be in unlikely places; such as going in sideways through an adjacent light.
I hope this helps!!!