It shouldn't be a problem. Just release pressure and raise temperature. Consider moving your beer back to fermentation tank. If fermentation will not start after about 3 days, you might meed to add a fresh yeast slurry. Best would be from the foam of primary on a similar brew. Carbonation is not good for yeast, but shouldn't kill them, either. It's a gamble if yours are alive and good enough. On the other hand, carbonation does not cause any permanent changes in beer, so once you get rid of it, fresh slurry will be able to finish the job.