excange rate changing

Dear all,

I have a PO and this PO currency not local currency. When I enter this PO in Miro , I use my local currency and I want to use different exchange rate each PO item. How can I do this in Miro or PO?

And when I change PO header exchange rate , this PO exchange rate not move in Miro. why can do this? when I fix the exchange rate , that time

exchange rate and PO currency automaticlly move in Miro.But I want to move only exchange rate. how can I do this?

Thanks in advance.