how to edit gridview in gridview row in c#?

Use [MSDN] GridView.RowEditing Event[^].

U want to edit on any button click (which is in main grid view) then here you have answer ,

 protected void btnAddGrid_Click(object sender, EventArgs e)
        {
            Button btnAddGrid= (Button)sender;

            GridViewRow grdMainRow = (GridViewRow)btnAddGrid.NamingContainer; // so u ll find main grid view row , from that find second grid view

            GridView grdSecond = (GridView)grdMainRow .FindControl("grdSecond ");
// now you can edit any row from grdSecond
}

If your answer is not this , then let me.