Each of the buildings with a puzzle slab has a sign with a letter label on the sign. There's 5 buildings and a 7 slab sequence you must press to solve the puzzle.
Here is a copy of the puzzle text:
Building A: A-B-_-_-C-_-A the o--er must -- res---t--.
Building B: _-B-D-E-_-_-A --- --der mu-- -- resp-----.
Building C: _-_-D-E-C-B-_ -he order ---- be re--e-ted.
Building D: A-B-D-E-_-_-_ --- ----- ---- be respected.
Building E: _-_-D-E-_-B-A the order mu-- -- ---------.
The full text is: A-B-D-E-C-B-A the order must be respected.
Once you push them all in sequence, the floor drops you into a previously sealed hidden room in the ruins where you can change a pokemon's Hidden Power by putting elemental plates into a basket. Warning: you have to swap plates, you can't just take it back.