Since you went to the area of the Luminous Order before, and met Cassedy there, the boot on the overview map to travel back and forth between the two areas should be in the south of Central.
If you have the quest, it should automatically trigger the next step when you get to the area I showed in the screenshot.
Unless you're on android, you could send me your save file to Naughty-Netherpunch@web.de so that I could check if you have some sort of bug. The saves are in the www/save folder. I only need one .rpgsave file with the save slot number in which you have the issue.