I've got the steps you need to update your WA Workers Comp rates for the existing Class Code in QuickBooks Online, accounting328.

1. Click the Gear icon at the upper right corner and choose Payroll settings.
   
2. Go to the Tax Setup tab.
3. Select the state for Workers Compensation Tax Setup.
    
4. Click the Add Class and Subclass link.
5. In the Risk Classification Class and Sub-classes then, enter the rate in the fields.
6. Hit OK once done.

Here are some pointers that you can check to learn more about how QuickBooks Online handles workers comp:

Understanding Workers' Comp Report.

Washington workers' compensation setup and calculations.

However, if you're still unable to update the rates, I'd suggest getting in touch with our QuickBooks Support. They have the tools requires to edit existing class codes and rates.

Please be reminded that our Support Team is available from 6:00 AM until 6:00 PM on weekdays, and 6:00 AM till 3:00 PM on Saturdays. Here's how to contact us:

1. Click the Help (?) icon.

2. Choose Contact Us.

3. Enter a  brief description of your situation in the What can we help you with? area, then click Let's talk.

4. You'll be presented with a few options for connecting with Intuit. Select Get a call.

I'll be right here to continue helping if you have any other concerns or questions about QuickBooks Online. Assistance is just a post away. Take care always.