Thanks for joining this thread, @ibizconsult.

The Inventory Adjustment that QuickBooks created will only pop up when you edit an inventory, just like your client did. If you change another inventory item, you'll see the pop-up message again.

In case you want to create an inventory adjustment account. Here's how:

1. Click the Lists menu at the top, and then choose Chart of Accounts.
2. Select the Account ▼ dropdown, and then New.
3. From the Other Account Types ▼ dropdown, choose Cost of Goods Sold.
4. Name this account “Inventory Adjustments."
5. Fill out other info as needed, and then click Save and Close.

Once done, you can now adjust the product’s quantity, value, or both. Let me guide you how:

1. Click Inventory at the top, and then select Adjust Quantity/Value on Hand.
2. Choose the Adjustment Type ▼ drop-down, and then select Quantity, Total Value, or Quantity and Total Value. 
3. Select the adjustment type option and then choose your adjustment account.
4. Enter the Adjustment Date.
5. Choose the Adjust Account ▼ drop-down, then select the adjustment account you set up.
6. Add Reference No. You can also assign a customer, job, or class.
7. Select Find & Select Items, and then choose the items you want to adjust. (If you have a lot, search for any product in the Find field.)
8. Click Add Selected items, and then add a new quantity or new value (or both) for each item.
9. Select Save and Close.

For more details, please check out this article: Adjust your inventory in QBDT.

Once done, you can run the Inventory Stock Status by Item report to check your product's quantity or the Inventory Valuation Summary report to know the product's value. This ensures your inventory is correct. Just go to the Reports menu, and then choose the said reports from the  Inventory section.

In case you want to adjust the inventory for finished products, you can refer to this article for the detailed instructions: Adjust inventory for finished goods.

Let me know if you have more questions about inventory management or any concerns with QuickBooks. I'll be glad to help. Have a good one!