Never tried it myself but someone posted this a while back. There are more posts about it but I have this one saved and copied it for you.
1.PREPARE MY LETTER. Empty envelope with their old address (my rental address) on the envelope just like I was trying to mail them a regular letter
2.PRINT “ ADDRESS SERVICE REQUESTED “ under the stamp.
3.MAIL THE LETTER normal procedure.
4.PO WILL FORWARD the letter
5.PO WILL ALSO SEND ME A POST CARD stating I have mail with $0.65 postage due.
6.Take the card to the post office and pay the $0.65
7.Post office will then write their new address on the post card
--107.147.xx.xx