How to update currency rates when a transaction is posted in a foreign currency?

Hello,

I want to post a transaction (e.g. Supplier Invoice) in a foreign currency and before completing the transaction (e.g., before paying for the invoice) I want to update the currency rates and run one currency revaluation to see how the system posts unrealized gain/loss to the GL on open AP.

Could you please tell me how to update the currency rates?

This is to be conducted in Apps 10 environment.

Thank you!