In quickbooks online I am trying to add a positive sales tax adjustment but the expense account I used previously doesn't show up as an available account.
I've got your back, @Jeff20. I'm here to make sure you can select your desired account for your sales tax adjustment.
Do you have an expense category named Cost of Goods Sold before? We can only select an expense account for positive errors, and an income account for negative ones. Since we have a separate account type specifically for Cost of Goods Sold, I'd suggest checking your Chart of Accounts list if there is an inactive expense category for COGS.
Navigate to the Accounting menu and select Chart of Accounts.
Click the Gear icon above the ACTION icon.
Put a mark next to Include inactive.
Type in "deleted" in the Search box, then press Enter.
That will show you all the accounts that you've marked as inactive. Check the screenshot below: