Ragnarok Mobile: Thief Job Change Guide
Thief: Melee physical damage dealers and famous for being... a thief! A bad reputation, but these slick handed thieves may one day become deadly Assassins!
When your character reaches Novice Job Level 10 then you can start the quest for your very first Job Change.
The quest will be given by the Knight NPC on the South Prontera map (Novice starting area). Just follow this quest and DO NOT accept any other quest. Ignore both Yellow and Green quest indicator on the map. Once the quest ask you to enter the Job Change Building... Good luck!