reflect Items on grid

Hello,

I have created a new form FormCT3. This form is header - Line format, Header Table is CT3Details and line Table is CT3Lines.

In FormCT3 , added a PurchId field on header from PurchTable. And when we select a PurchId in header then related Items from PurchLine Table is reflect to Grid on SubForm (i.e. Line Table).

Please help me…

Thanks