if clause problem

if Ext No: <input name="ctl00$ContentPlaceHolder1$txtextno" type="text" id="ContentPlaceHolder1_txtextno" /> is not hod then i want other textboxes to populate with hod email for their approval according 

how to do it use if clause 

or how to to select 

if(textbox.text=it01)

select it hod's email only