Salamun Market is only available in Warzone matches. You can set Salamun Market as your preferred map for Warzone in the Main Multiplayer menu. Your faction(s) will need to successfully complete the Search & Destroy objective as the attacking side, once as the ISA, and again in the next game as the Helghast, therefore you need to play a minimum of 2 games. Once you or your team has completed the objective as the second faction, the trophy will unlock. You don't have to personally plant the charges, just as long as your team wins that objective.