Conditionally update value of GridView Row based on DropDownList selection in ASP.Net

Dear All,

May i know how to update each data in gridview from template field textbox?

if select reason is adjust-In then update plus the qty else adjust -Out minus the qty. 

<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3A64F2" HeaderStyle-ForeColor="White" runat="server" AutoGenerateColumns="false">
            <Columns>
             <asp:BoundField DataField= "RowNumber" HeaderText="RowNumber" />
                <asp:BoundField DataField= "INV_ID" HeaderText="INV_ID" ItemStyle-Width="150" />
                <asp:BoundField DataField= "INV_TYPE" HeaderText="INV_TYPE" ItemStyle-Width="150" />
                 <asp:BoundField DataField= "INV_SHORTDESC" HeaderText="INV_SHORTDESC" ItemStyle-Width="150" />
                  <asp:BoundField DataField= "INV_LOCATION" HeaderText="INV_LOCATION" ItemStyle-Width="150" />
                  <asp:BoundField DataField= "INV_QTY" HeaderText="INV_QTY" ItemStyle-Width="100" />
                   <asp:TemplateField HeaderText="Adjust Qty">
                    <ItemTemplate>
                        <asp:TextBox ID="Inv_AdjQty" runat="server" />
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>

 protected void Page_Load(object sender, EventArgs e)
        {

            string conString = ConfigurationManager.ConnectionStrings["CIMProRPT01ConnectionString"].ConnectionString;
            string query = "SELECT ROW_NUMBER() OVER (Order by A.INV_ID,A.INV_TYPE,A.INV_SHORTDESC,B.INV_LOCATION,B.INV_QTY) AS RowNumber,A.INV_ID,A.INV_TYPE,A.INV_SHORTDESC,B.INV_LOCATION,B.INV_QTY  FROM CIMProRPT01.dbo.OTH_INV_DETAILS A JOIN CIMProRPT01.dbo.OTH_INV_QTY_LOC B ON A.INV_ID = B.INV_ID WHERE 1=1  and A.INV_TYPE =@INV_TYPE ORDER BY A.INV_ID,A.INV_TYPE,B.INV_LOCATION";

      
            SqlCommand cmd = new SqlCommand(query);
            cmd.Parameters.AddWithValue("@INV_TYPE", ddlCountry.SelectedItem.Value);
            using (SqlConnection con = new SqlConnection(conString))
            {
                using (SqlDataAdapter sda = new SqlDataAdapter())
                {
                    cmd.Connection = con;
                    sda.SelectCommand = cmd;
                    using (DataSet ds = new DataSet())
                    {
                        sda.Fill(ds);
                        GridView1.DataSource = ds;
                        GridView1.DataBind();
                    }
                }
            }
        }