To uncurl, I boil straighten. The water should be hot, but not extremely hot, or it could damage the hair. After drying carefully with a towel, or blow dryer (some people don’t use blow dryers, because the heat from it can melt the hair, but I find that if you’re careful, and keep it somewhat away from the hair and occasionally turn it off to comb out and feel the dolls hair for any remaining moisture, it should be fine) use a fine toothed comb, and comb the dolls hair. The comb I use is two ended, meaning on end is fine toothed, and the other end has average teeth size? lol.
To de-tangle the hair, just carefully and continuously comb the hair with the fine toothed comb. You want to be careful, because the comb WILL pick out knots, and if you pull or yank too hard, it can rip out the hair badly, and possibly damage the holes where the hair is rooted. Just keep combing the hair until you are satisfied with the results.