Hi Anusha,
First of all you should use the excel importer module to import the currency and the conversion rates.
https://marketplace.mendix.com/link/component/72
Follow the documentation on setting this up to import the excel.
Then you should save your currencies and conversionfactor in a different entity. The request should be associated with a currency. This allows you to select a currency using a reference selector and then accessing the conversion factor.
Hope this helps!