Hi PerspectivePlumb,
When lodging BAS/IAS in QuickBooks Online it must be from oldest to newest. You can record your IAS for July and August however we'll need to unlodge first your recent BAS/IAS lodgements.
There are two ways on how you can unlodge your BAS, you can either contact our support team or contact an accountant user. I'd suggest getting in touch with them since they have the facility and be able to unlodge it for you.
Feel free to drop me a reply below if you have any other BASIAS concerns in QuickBooks Online. I'd be more than willing to lend you a hand.