La Yuri and El Polito are the two people that must be killed in order to finish the last mission in Itacua region. First, you must find and break into their hut. You can find it, more or less, in the center of the yellow circle showed on the minimap.
To open the door's lock, use the interaction button. When you are inside, order your team mates to join you. Otherwise, they stay outside and won't help you in the fight.
Finally, you get to the room where your targets are. But don't shoot them through the glass because they are bulletproof. While crouching, go from the windows to the door. Before you enter the next room, remove the silencer to deal more damage.
When you are inside, kill the soldiers or they will kill you. La Yuri and El Polito won't run away far from you so you are be able to finally catch them.
When you kill both of them, the last mission in this region is over. This unlocks a new one.