How can I update the exchange rate date on the distribution line for all lines without entering each

Create a po with multiple line with usd currency on sep 13 2013

change the currency to euro

enter the exchange rate date

go to tools and convet currency to euro

 

now we are on 4 oct 2013

I need to change the exchange rate date on the distribution line

I have around 100 lines

so how can I change the exchange rate date on the distribution line without entering each line of the distribution