A friend asked me how to set exchange rate manually in MIRO. Of course this is applicable only for foreign currency purchase orders. The technique goes like this:
1) Go to MIRO
2) Enter Invoice Date, posting date, reference number and the foreign currency.
3) Go to Details tab page & enter the desired exchange rate.
4) Enter the PO No & Press Enter
It does work!
Thanks to my friend and the one who gave me the answer in the following link.
Aroop's notepad 