This achievement is a little tricky. When you first arrive in Prague, you are given two missions, one of which is to go see Koller. Before doing that, you want to take the metro to the northeast station. When you exit the station you will see an electronics store across the street in front of you. Circle to the right of the store and jump over the first wall on your left to find a manhole cover. Descend and you'll see a red area on the map to your left. If you approach the door, you're told to get lost.
There are a couple of ways through this, depending on your approach, but if you go through a tunnel back and to the right of the door, you'll find a door you can hack that lets you into the back area of the enemy zone. You can dodge a camera and drop into an underground tunnel to bypass the main casino area. Find another door to hack into a storeroom, then use the vent to go upstairs. In the room the vent empties out into, take out the guard (and possibly another one outside the room), then find a way into the safe in the corner to get the Neuroplasticity Calibrator.
An alternative approach is from the area of the exterior door where the guard sent you packing, you can work your way up onto some pipes and go right over him and through a vent into the corner of the balcony of the casino
Either way, once you've got the the calibrator, exit the area and then complete the main quest to find Koller. Once you're done that, he'll tell you he needs the calibrator...give it to him and the achievement will unlock.