You can turn on compulsory costing for an individual account from the account record.
For Standard Nominal
Click Financials, Accounts
Select the account.
Click Edit
Select the Compulsory Costing check box.
Enter a Cost Centre.
Click Save.
For Advanced Nominal
Click Financials, Chart of Accounts
Select the account.
Click View
View the record.
Select the Compulsory Costing check box.
Enter a Cost Centre.
Click Save.