Generally your text is converting to kannada when your focus moves from the respective textBox.
So on your design page, double click on the button , the aspx.cs page ll be opened with this tag-
protected void Button1_Click1(object sender, EventArgs e)
{
}
Paste the conversion code here, then u can achieve the same with button Click event.
Gotaitu ankotini..:-)
All the very Best