Pick a chapter in the middle and if it's something you've read before, you'll start remembering the early stuff. Pick a chapter in the middle of the middle chapter and the latest chapter, and if it's new, go back half way to the last read chapter; if it's old, go forward to the middle of that chapter and the latest.
That way you don't have to reread everything and the skips put you closer to the latest chapter.
If you scroll to the chapters thingy (the one where people upload chapters) last thing you read would be grey and anything you didn't would be white :3
Forgot which chapter i read last time, but too lazy to reread from the start