try this :
combobx1.Text = "India"
but if you have a datagridview it's different :
to create it by code :
string[] str = {"Chennai","Bangalore","Trivandrum","India","US"};
DataGridViewComboBoxColumn cmb = new DataGridViewComboBoxColumn();
cmb.HeaderText = "Headertext";
cmb.Name = "name";
cmb.MaxDropDownItems =str.Count() ;
foreach (String o in str)
{
cmb.Items.Add(o);
}
dataGridView.Columns.Add(cmb);
then to change the text you should use :
for (int i = 0; i < dataGridView.Rows.Count - 1; i++)
{
dataGridView.Rows[i].Cells[where the combobx located].Value = "India";
}