Next step intent to foreclose tax lien comes back undeliverable

[Karen D. Schiano]

New to foreclosing vacant land in Navajo Co, Arizona.  One of my tax lien Intent to foreclose notices came back "vacant", another "undeliverable as addressed, unable to forward" (both addresses were addresses on file with Navajo County and where notices had to be sent).  I assume I must try to track down the owners or heirs, if deceased (one is deceased) and send new Intents to Foreclose with new 30 day or greater dates with intent to file the foreclosure action?  Or can I just file the foreclosure action to the heirs of the deceased "vacant" one (I have found them, having talked to a relative who gave me the heirs' names) without sending a new intent to foreclose?  Does anyone have experience with this?  Thanks.