File association help

I have files that are exported from our accounting program. When I first went to look at these files they were not associated with any program. When I told windows to look for a file to open it with, I accidentally (stupid I know) checked the box to always use that program to open it with. I need to see the files the way they were originally, not just try to associate them with a new program. I have tried re-exporting to new locations and of course this doesn’t work. Does anyone know how to turn this file association off?