Can we change the invoice no series format currently i use it as AC/23-24/0001 Need to change it to AIT/0001/23-24 how can this be done ?

Yes, you can, hasmatziaa. 

Changing the format of the invoice number series can be done in a few easy steps. Just turn on the Custom transaction numbers from the Settings menu. This allows you to modify the desired invoice format.

I'll guide you on how to accomplish the tasks:

1. Go to the Gear icon and select Account and Settings.
   
2. Pick the Sales tab.
3. From the Sales form content section, click Custom transaction numbers and turn it on.
4. Tap Save, then Done.
   

Moving forward, when creating new invoices in the future, the system will follow the sequence of the newly modified invoice series.

The program also lets you change sales form content to display what you want. For more details, check out this link:  Customise invoices, estimates, and sales receipts in QuickBooks Online.

Please let me know if you have other questions regarding managing invoices in QBO. I am always available to assist.