Adding Exch. Rates manually in currency table
Go to search and type Currencies and click on link under Go to Pages and Tasks
Select the required currency code and click on Process > Exch. Rates
Click on New and populate the following fields in the line:
Starting Date: date
Exchange Rate Amount: rate for the day
Relational Exchange Rate Amount: 1
Adjustment Exch. Rate Amount: same as Exchange Rate Amount
Relational Adjmt. Exch Rate Amt: 1
Fix Exchange Rate Amount: Relational Currency