Hi Melissa,
Only accountants have the option to unlodge a BAS period in QuickBooks Online. If you do'nt have the unlodge BAS option in the QuickBooks Online file, I recommend contacting our Customer Care Team to help you unlodge the BAS period affected. They have the right tools to help you reverse the BAS.
Check this link to learn more about: What to do when BAS amounts look incorrect.
Post again in the Community if you have other questions about unlodging your BAS.