Hi there, sgobeauty.
It seems this is a related post on another thread. If you're referring to turn off the auto-fill option for Check numbers, this isn't available in QBO. However, we can delete the check number on the field.
For now, we can take this as a product suggestion. You may consider checking out our Video tutorials for QuickBooks Online.
I would also recommend visiting our Blog site. From there, you'll be updated with the features and enhancements that our developers are currently working on.
The Community is always here to help.