I'll share some insights about adding a discount to an individual product @rbfmachineservic and guide you on how to do it.
Adding a discount to a specific item in QuickBooks Online (QBO) is unavailable. However, you may consider using a discount service item which you can add to invoices or sales receipts.
Follow the steps below:
Go to the Gear icon, then select Product and Services.
Click New to create a new item.
Choose Non-inventory or Service for the type.
Name the item Discount.
In the Sales price/rate input the discount as a negative value.
In the Income account drop-down menu, select the Discount given account.
From the Tax drop-down menu, select Nontaxable.
Save and close.
Once done, apply the discount when creating an invoice or sales receipt.
Here's how:
Click the + New button, then select Invoice or Sales receipt.
Fill out the details and add the Discount item you just created.