Defeat Sanja Gusts southwest of Dimita Oasis in Tabazra Desert, then talk to Guard Ruslan at Tabazra Post. Use your quest tracker to see your progress.
Guard Ruslan: I have more information for you. It's about a bounty. HiiragiKagami: Great!! NakanoAzusa: Sigh... Guard Ruslan: Direct threats to Dimita Oasis are sanja gusts. Guard Ruslan: The Congress has issued an announcement Guard Ruslan: to mercenaries that ones who defeat the sanja will Guard Ruslan: get rewarded. If you defeat them instead, you'll be Guard Ruslan: able to get the reward. HiiragiKagami: Let's go and defeat the sanja gusts!