How to populate the value in FlowField?

Hi all,

I have created a header table and line table. In line table, there is a field named "target price" and I have created a flow field in header table for "Target price".Finally I have created a Header line form. In the line form, I am entering the target price and after entering it i should find the value in header form getting updated automatically without clicking on it. is it possible to populate the flowfield in header form without clicking on it?

thanks in advance.

regards,
chandru.