Welcome to the Community, @Anil.
Giving your customers account IDs will help you keep your QuickBooks Online accounts organized. It is entirely up to you if you put it or not, as there will be no discrepancies whether you include or exclude customer IDs from existing customers.
If you want to add customer's IDs, you can follow the steps below:
- Go to the Customers tab.
- Select the specific customer, then click Edit.
- In the Customer display name field, enter the account number before the customer name.
- Select Save.
For more detailed steps and information, you can refer to this article: How to assign account numbers to customers in QuickBooks Online.
If you need to update your customers' credentials, please see this article: Add and manage customers in QuickBooks Online.
Keep me updated if you have any additional questions or concerns about your customers. We're always willing to assist. Have a wonderful day.