it's easy, just showing my QR code to ticket, and change tickets, they give 2 tickets. and insert it all together. and it will remain 1 ticket to bring and for check out in Narita.
important do not lost your previous ticket, I go from Tabata station, yamanote line, so do not exit the other exit. you must exchange ticket to Skyliner.
i remember last year have to pay alot because i can't show the ticket.