Hello @jennie9832,
Thank you for posting here in the Community. I can help you void checks and create new ones in QuickBooks Online.
You can find the existing checks under the Expenses section. From there, you'll have an option to void each transaction manually.
Here's how:
- Sign in to your QuickBooks account.
- Go to the Expenses section.
- Find the check.
- Click the View/Edit drop-down arrow.
- Select Void.

Once done, you can proceed with creating the new checks. The option is available when you click the + New button on the dashboard.
Please follow these steps:
- Click the + New button in the upper-left corner.
- Select Check under Vendors.
- Fill in the necessary information.
- Hit Save and close.
If you're referring to payroll checks, I recommend following the instructions in this link: Delete or void employee paychecks.
Additionally, I've attached an article you can use to modify transactions directly in the account register in QuickBooks: Find, review, and edit transactions in account registers in QuickBooks Online.
Drop me a comment if you need further assistance voiding transactions in QBO. I'll be more than happy to lend a hand. Have a great day!