Hi Felliottau,

Thank you for your inquiry.

If you would like to adjust the casual rate loading, please use below steps:

1. Select the Employee tab from left-navigation menu
2. Go to Payroll Settings tab
3. Under Pay run settings column, select Pay Categories
4. Click the casual pay category to review the oay category detail
5. You can adjust the % under rate loading columnI 

I also found below article which is written by KeyPay, the payroll provider in QuickBooks Online, which outlines the process to adjust casual rate loading.
https://yourpayroll.zendesk.com/hc/en-gb/articles/202437454-Adjusting-Rate-and-Penalty-Loading-on-Pa...

Should you require any assistance or have any questions, please don't hesitate to Click Here to our Live Chat window and our support representatives will be more than happy to help!

Thanks Felliottau, have a great day!