Hello there, dan_air1.

Resetting invoice numbers in QuickBooks Online is unavailable. Instead of doing it, you can turn on the Custom transaction numbers feature to change the number of previous invoices. Here's how:

1. Go to the Gear icon.
2. Select Account and Settings under Your Company.
3. In the Sales tab, enable the Custom transaction numbers feature under the Sales form content section.
4. Click Save. Then, Done.

Once done, we'll see an Invoice no. field where you can enter your own numbering preferences. We can also open the past invoices and modify the number.

I'd like to include some articles that will guide you through customizing, attaching files, and emailing sales forms in QBO:

• Email and customize sales form.
• Add, customize, or remove logos on sales forms. 

Let me know if you have other questions. Take care and stay safe always.