Campsite warp to the 'L' on your map (if you’re far away) and you’ll meet up with Luisa once again. Join her by riding shotgun on her carriage and when you reach the destination, you need to run around the side of the fort and climb over the broken part of the wall (as indicated on the radar by a yellow dot).
Run up to the sniper point - indicated by the usual yellow cross - and pick up the sniper rifle. Aim down the sight and take out the guard standing by Reyes (who’s tied to a post at the very far end of the courtyard).
Once you do this, all hell will break loose, so switch back to your best standard rifle and head back down the way you came. Now target the TNT crates stashed all around the courtyard to help make light work of the guards who’ll all be shooting at you.
Once you’ve killed them all, go to the main gate and call your horse to you. Now take it to Reyes and he’ll jump on board with you. Now you’ll meet up with a guide outside so press onwards at full pelt towards the target on your map.
Have your rifle to the ready as you’ll be ambushed by numerous troops as you follow the guide down the dusty trails. You can shoot them all when they appear in front of you, or you can try and dodge past them, the choice is up to you.
Once you hear that Luisa is waiting for you, your destination on the map will change, so watch out for it (as it’s easy to miss the change). Get Reyes to Luisa to complete the mission!