After you turn on multicurrency (which you can do from a web browser by following the steps here), you can choose who pays you with a foreign currency.
- From the main menu, select Customers +.
- Fill out the customer's details.
- Under Customer Pays Me With, and choose the currency.
- Select Done.
Read more about multicurrency here!
Note: Use the same steps to assign a foreign currency to a supplier, select I Pay This Supplier With, and choose the currency.