You must have completed Seth’s first mission 'Exhuming and Other Fine Hobbies' before this becomes available to play.
Meet up with Mr. Dickens again as he persuades you to join him in another one of his wily sales pitches. Jump into Dickens’ cart and you can listen to the conversation if you want (or you can simply skip it with a press of B/Circle).
The race is very similar to the one you had earlier with Bonnie, where you’re racing line will be indicated by burning fires. By now, you’re abilities to keep a horse running at speed without using much - if any - stamina should be pretty good.
So use the same rhythm here as before and you should have zero problems getting to the front of the pack (and staying there). Watch out for any hairpin turns and simply stay alert and you should win this race with zero problems on your first try.