@AbegailS_  RE: With the new invoice layout in QuickBooks Online, duplicate invoice numbers aren't allowed. 

That's really stupid. What is wrong with the QuickBooks Online development team?

You also didn't answer the questions.

The questions are, "How do we change an invoice number?"  and "In desktop version it just went to the next number. How do we duplicate the desktop solution?"

They're really short and simple and don't use any big words.  Did you even read the questions?