If you want to convert the prices of price list items in the home currency using the relevant foreign currency exchange rate, you need to set up exchange rates for pricing.
If no pricing exchange rate is specified, loading a foreign currency into a document will not trigger any price recalculation for the items.
The exchange rate is not updated automatically. It must be entered manually and updated as needed (or a new one created from the relevant date).
You can find the pricing exchange rates at the following path:
Tools -> Codebooks -> Pricing Exchange Rates
If an exchange rate is no longer current, there is no need to delete it. Simply create a new one with a validity date starting from a more recent date.

