In this configuration activity we are able to assign a number range to an account group for customer master data.
IMG Path: Financial Accounting (New) -> Accounts Receivable and Accounts Payable -> Customer Accounts -> Master Data -> Preparations for Creating Customer Master Data -> Assign Number Ranges to Customer Account Groups
Tables: T077D, T077X
When you open the transaction you will get a list of all account groups created for customer master data. Find the desired group and assign a number range to it.