I need help getting air bubbles out of my framed poster?

I used modge podge to adhere the poster to the cardboard backing, and when it got really humid air bubbles appeared. I really don't want to re-do the entire project, so I was wondering if there was any way to get the air bubbles out and prevent them from reappearing? I also know now that I should have used an acid free spray adhesive in the first place, and I'm wondering if there's still a way to use one to save the poster?