After helping Zizi Time Witch in Al De Baran to help him revenge against her foe who stole her the Time Wand. You’ll be asked to find this little guy in Clock Tower 1F.
This is one of the Exploration quest in Ragnarok M Eternal Love (Mobile) and there is no in-map guide to find Little Marty.
If you still stuck on this quest and still keep looking for the little Kid, he is just
Talk to him to start the quest Time Witch Quest.
You may also check the video game walk-through for reference.