You must ensure you do the Douglas Bounty and collect Sweezy before attempting the Krubis Bounty! During the Krubis bounty you'll run into an Administrative office run by Moplets. You need to be carrying Sweezy to unlock a third dialogue option "I'm the new boss" for the achievement to pop.
Start Krubis Bounty
Use "I'm the new Boss" option when speaking to the receptionist
Any dialogue options after this are your own choosing.
If you have completed the Krubis bounty first, unfortunately you'll have to start a new game to unlock this.