I'm here with some instructions that make changing the account for your products a breeze, @amarcano.

To update the past transactions when changing the account for your product or service item, you have to check the box for Also update this account in historical transactions option. Here's how:

1. Go to the Sales menu and select Products and services. 
2. Look for the item you'll need to update. Then click Edit. 
3. If you don't see the Also update this account in historical transactions box under the Sales price/rate field. Do the next step. 
4. In the Income Account drop-down, type the name of the correct account or any account in the list. For example, enter the word "income". 
5. Once you click an account, the Also update this account in historical transactions checkbox will appear.
6. Check the box.
7. Then, go back to the Income account drop-down and choose the correct account. 
8. When finished, hit Save and close to confirm the action. 

Here's the article that will provide info about the process: Change the account for a product/service item. 

Also, you can pull up inventory reports in QuickBooks Online to see your best selling items, what’s on hand, the cost of goods, etc. 

Don't hesitate to post again here if you have any other concerns about changing the accounts of your product items in QBO. I'm always here to help. Have a great day ahead.