User has created some write-off payments and these transactions are getting logged against the Default Item Expense Account. But the user wants to specify a Bad Debt account for these transactions and has already created an expense account for this.
To log your write-off or credit payments against a specific account instead of the default one, you need to select that account as the Posting Account when creating the payment. In the Add Payment screen, when you select the payment method as Write-Off or Credit, the Posting Account drop-down appears. Select the account that you have created for logging write-off or credit payments from this drop-down, apply the payment and save the changes. The payment gets logged against the specific account. Check CORE Help Center for details on creating write-off or credit payments.