Thanks for posting in the Community! There are two ways on how you can unlodge your BAS. You can either contact an accountant or our customer support team as they have the facility to undo a lodged BAS in QuickBooks Online.
Here's how to contact us:
Click on the Help (?) icon.
Select Assistant and enter Contact support in the chat field, and then click the Send icon.
You'll be asked about your concern, and you'll need to enter and send it.
If you can't see any related topics to your issue on what they shared, select No, get me a human.