How to change the invoice number on sales forms?

Hello @rajithsam-r,

Nice to have you in the Community. I'm here to lend a hand with changing the invoice number on sales forms. 

QuickBooks Online can have customized numbers for sales forms, including invoices. Here's how to enable it:

1. Select the Gear icon.
2. Click Account and Settings.
3. Select Sales on the left.
4. Click the Pencil icon in the Sales form content section.
5. Place a check-mark in the box next to Custom transaction numbers.
6. Click Save and Done.

Once this option is selected, you will have the ability to edit the number that's used on a sales transaction.  The following is a picture to serve as a visual reference:

For additional insight into this, such as how to modify individual transactions, please see the following article: How to Change the Invoice Number on Sales Forms.

That should take care of it. These resources should assist you with changing the invoice number on sales forms. 

The Community is here anytime you need it, so feel free to let me know if you have any questions. Wishing you success in all your endeavors.