tell it you aren't going to use it anymore.
"yeah, you think you're so smart, particle board, I ain't gonna use you next time...whaddaya think of that? That'll fix ya!"

sorry for the silliness. Try this
use that piece as a template and cut a new piece of particle board and just replace that section. You could try squashing it in a vise, but once it expands, it'll be weaker in that area for as long as you have it, even if you can squash it back to it's original thickness, and it'll be more "flakey" than particle board already is.