Find Ajax WaterMark textbox inside a repeater

void Repeater_ItemDataBound(Object Sender, RepeaterItemEventArgs e) {

        
          if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem) {

             
           TextBoxWatermarkExtender txbWaterMark    = (TextBoxWatermarkExtender )e.Item.FindControl("RatingLabel");


//if(some condition to check whether textbox contains airport )
txbWaterMark.WatermarkText= "airport";

//if(some condition to check whether textbox contains airport )
txbWaterMark.WatermarkText= "railway ";

             }
          }
       }