Note - it is possible to complete the sixth chapter only after you have completed the game's story mode.
You need to return to Celia's apartment in Uptown. Interact with the marker to connect to your inFamous Paper Trail profile. If you have performed all of the steps, on the game's web site (reading the secret correspondence after breaking into the computer) you will be allowed to start the last, nineteenth mission. Press UP on the D-Pad and start the final chase after Celia. The premises of this one are the same as in the case of the ones that you took earlier so, you cannot lose it, because Celia will be stopping on a regular basis and waiting for you to catch up. During the chase, use the Neon, or the Video powers, thanks to which you will not have any problems reaching the rooftops.
Towards the end of the chase, Celia escapes to one of the balconies of the tower that you have visited in the 17a or 17b mission. To get to the spot that she is in, you need to switch to Smoke and use the nearby venting shafts.
Celia escapes into the tower and you need to approach the door located on that balcony, to join her. After you get into the arena, where you fought your final battle with Augustine, pick up the last Origami Dove), which will start the final cutscene connected with Celia.
Wait until you return outside. As a reward for completing inFamous Paper Trail, you gain access to Delsin's several new outfits. The most interesting is the one that makes Delsin resemble a bunny. Congratulations
Note - if you want to, you can log on to the inFamous Paper Trail web page again and see the last Origami Dove #21, but you do not receive any additional rewards for that.