Keep in mind, these missions have a LOT of variables.
Just because someone points out a certain house and a certain task to get access to that certain house, does NOT mean it will be the same house or the same task for you.
Make sure you have the mission Tracked/Followed, from the Side Mission Log in the menu, off to the right from the map and inventory screens. If the mission is Tracked/Followed, you should get hints about where to look. If not, you may have to go house to house.
You might find a house with barricades, junk piled up in front of the doors…might have to use explosives (walk up to the obstacle, interact with it, it’ll say something about using some explosives—the same type you use for crafting ammo, etc) to blast the barricade and clear the way to the door…
Or you might be able to walk up to the doors and interact with them, but they give you a message like “blocked from the other side” or some such—if you find a house like that, every exterior door for that house might be blocked like that…or you might find one door that IS open, and then you’re in and on to the next step.
You might find that one of the interior doors is blocked, locked, so you’ll have to go back outside and find a way to shoot something in that room, through a window, to gain entry.
You might even find a house that has no way to enter from the ground level, so you may have to climb up on top of something and gain access through the second story—jump or climb to the balcony, or to the roof and then climb/fall to the balcony…
As with any thorough search, take your time, look at everything. Secure the area first if need be, destroy any nearby machines in the area if there are any, so you can take your time and stand fully upright and search at your leisure…you may have to jump around some…then check every door, look up at every second story, check any possible access points at all, look carefully at anything that might be blocking a door, interior or exterior, to see if there is some interaction point.