Yes, those instructions are for the Desktop version of QuickBooks, Page Custom Supply LLC.

I can provide the steps for the Online version of your account. When you import products and services in QuickBooks Online, there's an option

to Overwrite all values for each product or service that you import with the identical name. Doing this will merge any imported Product or Service with the same name as an existing one. Here's how you can achieve this:

Importing Products and Services

1. Click the Gear ⚙ icon, then Import Data.
2. Select Products and Services. 
3. Click Browse and find the file containing your items.
4. Follow the on-screen instructions to map and upload your data.
5. On the screen that lists all of the Products and Services to be imported, check the box at the bottom if you'd like to Overwrite all values for each product or service that you import with the identical name.
   
6. Once finished, click Import.

The system will create an automatic Inventory Adjustment if a different quantity is being imported. Check out this link for your reference: Import products and services from Excel.

Also, you can use the audit log to see how it affects the existing product.

Leave a comment again if you need anything else. I'll always up to help you with importing products and services in QuickBooks.