Find selected row of RadGrid on buttonclick

 protected void btn_submit_Click(object sender, EventArgs e)
    {

        foreach (GridDataItem item in RadGrid1.SelectedItems)
        {          
            string custoID = item.GetDataKeyValue("Branch_code").ToString(); //you have to set DataKeyNames value to the column whose value you have to find
        }
    }

Find and Update Control Values before InsertForm of Radgrid Opens

Suppose if You wants to change RadDatePicker Min date which is inside insert Item

So before the form OPens You can change this value On RadGrid Item Command

 protected void RadGrid3_ItemCommand(object sender, GridCommandEventArgs e)

    {

        if (e.CommandName == RadGrid.InitInsertCommandName)

        {

            e.Canceled = true;            

            System.Collections.Specialized.ListDictionary newValues = new System.Collections.Specialized.ListDictionary();            

            e.Item.OwnerTableView.InsertItem(newValues);

            string selected = RadYear.SelectedItem.Text;

            GridEditableItem insertItem = e.Item.OwnerTableView.GetInsertItem();

            RadDatePicker dtt = (RadDatePicker)insertItem.FindControl("RadDatePicker3") as RadDatePicker;

            dtt.MinDate = Convert.ToDateTime(selected + "-01-01");

            dtt.MaxDate = Convert.ToDateTime(selected + "-12-31");

        }

    }