I'd take a stab at it. I'm sure you will get more expertise to follow. What I would do first is decarbonate it. I would rack it into a carboy or bucket, and let it sit for a while (maybe a week?), at room temp, with no air lock, maybe just an empty s-shaped airlock. I wouldn't be too concerned about contamination because after all, it is beer, and the alcohol helps protect it. Then, I'd make a starter, repitch the yeast and give it about two or three weeks to finish, all the while being excited about how it will taste. Good Luck!