Convert from Naira to

I have enabled naira for woocommerce (Wordpress) even when Paypal is enabled, using some code in functions.php. But when the payment redirects to paypal it defaults to dollars. I want to set the exchange rate from my dashboard and send the equivalent to paypal e.g. When cart has N1000 it becomes $1000 when it should be about $5. I want to be able to set the exchange rate from Naira to Euro, Dollar and Pound in the Backend. The calculation from this exchange settin is what paypal gets depending on the currency user chooses. I have a payment gateway that only supports naira too so I want the reverse too? i.e. when $ (or pound or euro) is the shoppers chosen shopping currency, the naira equivalent should be sent to this gateway. This is a plugin I expect to be able to install on any wordpress website.