The History view of the Account Information window should be displayed. (To find the Edit Accounts window - History view)
Exception: You can't enter an historical balance for the Current Year Earnings account
There is one exception to this rule, however: If your conversion month occurred at the beginning of a new fiscal year, you can enter historical amounts for your income, cost of sales and expense accounts for the month preceding your conversion month.
Warning: P&L accounts' historical opening balances will be changed by additional historical entries