If processed pie filling does not seal, you can either store it in the fridge, use it to make a pie, or reprocess it. However, before you reprocess it, check to make sure you have enough headspace. Most likely, the apples expanded as the filling heated up in the water bath. You may need to remove some of the filling to allow for expansion. Using inferior lids/rings can also cause jars not to seal. I have found this to be true with the lids I purchased on Amazon. Make sure you are using new, name-brand lids, Ball lids, for example.