In your web console, navigate to the main menu item 'Settings', and then to the drop down menu item 'Exchange Rates'.
On this page you'll see a list currently available.
Navigate to "Create" in the title bar, and this will bring up a new orange dialogue box for you to create your new exchange rate.
1) Source Currency
From the dropdown menu, choose your source currency to which the exchange rate will be applied.
2) Target Currency
From the dropdown menu, choose the target currency.
3) Start date
From the date picker, choose a start date.
Manually enter an exchange rate amount.