Hello there, r39moore.
Thank you for posting here in the Community. I'd be happy to lend a hand with changing markup in QuickBooks Online.
If you're trying to change the markup default rate, you can go to the Account and Settings section.
If you want to change the markup on a transaction (bill, expense or check), you can edit them through the Expense Transactions window.
You can follow these steps:
For more information you can also visit this article: Enter billable expenses by job.
Please be sure to let me know if you need further assistance with the Markup feature. I'm always available here to help.