You do not have to enter the exchange rate used in reporting foreign account information in TurboTax. You will enter the US dollar equivalent based on the exchange rate you used. You should keep a record of the rate you used.
TurboTaxDavidD offers the following advice:
You have a choice of which rate to use, so use the one that is most beneficial to you. According to the IRS:
Use the exchange rate prevailing when you receive, pay, or accrue the item. If there is more than one exchange rate, use the one that most properly reflects your income. You can generally get exchange rates from banks and U.S. Embassies.
The IRS also lists the following resources for obtaining an exchange rate:
Governmental Resources