He knew how to enter with the original lab.
View attachment 3465221
See?
It's the same method... Bottom right corner, face a wall and hit enter.
The two of you said the same thing, with your minor elaboration resulting in "do the exact same thing as before" which is still the same as what PBS666 said.
At worst he'd go to the very bottom of the new lab, and when that doesn't work the next logical thing to do would be the only other possible lower right corner... It's not rocket science or some sort of specialist skill.