There is option in "GridView" to give "DataKeyNames".
This "DataKeyNames" itself suggests what it is.
For your requirement you can store the "DealerId" in it.
Code is like below
<asp:gridview id="grdDealerDetails" runat="server" autogeneratecolumns="False" allowpaging="true" datakeynames="DealerId" .....></asp:gridview>
The DataKeyNames is the same as of the primary key name of the dealer table.
And when you save the details to the database you can get the PK of the selected row in GridView automatically. To get the "DealerId" follow the code below in RowUpdating event.
protected void grdDealerDetails_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
int DealerId = Convert.ToInt32((grdDealerDetails.DataKeys[e.RowIndex]).Value.ToString());
}