Final answer:
Zelgon Inc. should reverse the original entry made for the write-off when collecting an account previously written off.
Step-by-step explanation:
When Zelgon Inc. collects an account previously written off by debiting Accounts Receivable and crediting Allowance for Doubtful Accounts, they should also reverse the original entry made for the write-off. This means they would credit Accounts Receivable and debit the Allowance for Doubtful Accounts. By doing this, Zelgon Inc. is able to accurately reflect the collection of the previously written off account in their financial records.