This is one of three missions available to you at one time. Note that after finishing two of these, the simulation will be overrun by a lot of gang members, so it would be wise to do the A Game of Clones to get rid of them.
This is Ben King’s simulation and at the beginning, just walk forward until the Vice Kings notice you and start attacking. The only problem is that you start with no weapons of any kind, but one of the initial Vice Kings will have a pistol, so you’ll grab that after killing him. After finishing off the first batch of Vice Kings, head towards the church and more will appear.
As you kill the Vice Kings here, make sure you go and pick up any weapons they drop so you will get some more firepower. When you’re told to enter the church, do so and explore the various nooks and crannies it tells you to until you meet up with King. At this point, Vice Kings will start pouring into the church, so fight them off with King until you are told to exit the church.
Once outside, you will have to fight off more Vice Kings, so keep doing that until Kinzie tells you she left a present for you in a shallow grave nearby. It turns out to be a RPG and while you may want to start using it on the Vice Kings, keep it until a little later in the mission.
At this time, Ben will decide to go on his own, but you will stay put and continue fighting off the Vice Kings in your area. Eventually, Kinzie will shout that King has went down and tells you to hurry there to revive him. Rush over there and pick him up, then keep killing the enemies that appear. Kinzie thinks about forcing both Tanya and Big Tony to spawn, but Tony decides to come on his own. A well placed shot or two from the RPG will quickly take Tony down.
With that all over, King wants to give Tanya one more chance to stop everything, so head back to where you first entered the simulation. Tanya refuses to give up and will start attacking, She has some super powers, so be on the lookout for thrown objects and her always moving around. If you still have the RPG, then use that to quickly defeat her. Once she’s dead, a cutscene will play and the mission will end.