How to pass value in screen:exchange rate

Hi Gurus,

1. I had added one field translation field in miro detail tab whose value is populating through posting date-1 for this i used screen exit.

2. According to translation date exchange rate value is populating for which i used implicit enhancement. Like when we give posting date in basic tab of miro translation field value is populating as posting date -1 and according to that exchange rate is fetching from table tcurr.

Now this all I achieved.

But there is one condition that when user want to change translation date manually greater than 01.01.8000,exchange rate should take value from tcurr table according to this translation that.How I will acheive this?

I used select query for that but the value  is not coming in the the field on screen.