Final answer:
The sales associate should inform the customer that the software is currently out of stock but can be pre-ordered. They can also suggest alternative options for completing taxes.
Step-by-step explanation:
To help the customer in this situation, the sales associate should inform the customer that the store currently does not have the software in stock but a new supply is expected soon. The associate should offer to pre-order the software for the customer so that it will be available as soon as it arrives. Additionally, the associate can suggest alternative options for completing taxes such as online tax filing services or seeking assistance from a tax professional.