In Quickbooks Desktop go to MENU > Company > Manage Currency > Home Currency Adjustment.
Select DATE and CURRENCY. Click on CALCULATE ADJUSTMENT. If relevant transactions are on record table will come up with accounts to adjust.
Check affected account and SAVE. See your new account balance.
Note: You will get empty output on table if foreign currency account balance (not USD balance on foreign account) is zero at selected date. In such case just change date according to some non-zero balance.