Epilog is a short additional quest for Kingdom Come: Deliverance, which is switched on after completing the main task of An Oath is an Oath and watching the final subtitles. This quest will not cause you any problems. It consists of just a few conversations and one long journey.
Immediately after the epilogue, head to the castle in Rattay. After reaching the courtyard, a longer cutscene will be shown. After watching it, talk to Sir Radzig and pick up the letter from Margrave Jobst.
You have to go on a trip with Sir Hans and your destination is one of the main roads to the north of the village of Neuhof. Meet Sir Hans in the courtyard, confirm your readiness and jump on your own horse. Caution - Errors may occur here, as a result of which Hans' horse may block on the fence, bushes or other objects from the surrounding area. Don't wait around then, just head north-east. The mission's objective should be updated automatically.
The purpose of the trip is the camp near the road as shown in the screenshot. Talk to Sir Hans there and confirm once more your desire to embark on a journey.
Important note - After you have spoken with Sir Hans for the last time, the game will run the final cutscene and display a text announcement informing you that the game has been completed. Then the game switches to the main menu. Fortunately, the game allows you to continue your adventures after the main plot has been completed (!). Decide to load the autosave from the beginning of the epilogue or from the moment you reach the camp site near Neuhof (screenshot above). Then, you can ignore the meetings with margrave or Sir Hans and continue your exploration of the world. This will also allow you to continue the development of your character. You may also try to finish all of the unfinished, optional quests.