Change the text in the dialog's init event:

Code:
dialog dns {

  title "DNS/IP"
  size 300 200 95 50
  option dbu

  text "" , 1, 10 10 75 7
  edit "", 2, 10 17 75 10
  button "Enter", 3, 10 27 75 10

}
on *:dialog:dns:init:*:{ did -a dns 1 Enter IP (default is %bot.ip $+ ) }