You can uncap each bottle to let some of the co2 escape and then recap them and pray they build up enough co2 to re-carbonate.
You could also try this which I will preface this by saying I have no actual experience trying to pasteurize beer, only cider but I see no reason why this would not work.
If you go this route then you will need to consume the beer within a few months I think, it won't age well.
Also the reason you are most likely having this problem is that fermentation was not finished when you bottled, you then added priming and the yeast are still eating away. Could also be that you added to much priming sugar, or that you have an infection.