When first arriving to the PCL in Chapter 3, Tim and Pikachu will need to solve the pass code that Wallace set on the door that leads to the courtyard. If they don't, they won't be able to further search for an Identical Vial to the one they found in Harry's Apartment. Nina, one of the researchers at the PCL, will Note that Wallace wrote an equation to figure out the pass code on the whiteboard in the Meeting Room, but it is far to complex for her to figure out.
If you the go to the meeting room, you will see a chart at the top right corner of the whiteboard. As you do, you will then be prompted to check the plants and books throughout the facility to help you figure out the new pass code. Since the plant in the meeting room will be of no use to you, you'll need to head to the library on the opposite side of the hallway you just came from.
By searching the plants found within the library, you will discover another piece to figuring out the code. From there, you should be able to figure out the entire pass code simply by reading the books on the shelves in the library. The pass code Wallace set is the following: Triangle (Rotom), Star (Garbordor), Diamond (Trevenant), Square (Fennekin).