If your prints are super tight cut the ends at a long tapered point that should let you get it through. If your prints are really bad see if you can scrape out the tunnel but from both sides. There is also a trick of using a flat head screwdriver to push it through one notch at a time. In the end though it is a bad print. The belt should be snug but still slide through.
Did you print them on their sides so that tunnel is two pillars not a large overhang?
If it is really bad you might want to do a little slicer tuning to get your retracts and cooling in line.