Hello there, @vinit2vinaya.
You may check the ABN (Australian Business Number) field using the Custom form styles feature in the QuickBooks Settings. Here's how to enable this field:
I've added this article to help you in the future to customise your sales forms such as quotes or sales receipts: Customise invoices, quotes, and sales receipts in QuickBooks Online.
Please don't hesitate to tag my name in the comment section below if you have other concerns or questions. I'm here to assist you further. Take care.