How to curl my handmade rag dolls straight acrylic yarn hair?

The hair is pink and black in colour, but my daughter whom I’m gifting it too has long curly hair and I’d like it to reflect part of her heritage. All the videos I’ve seen have been curling the acrylic yarn before attaching it to the doll, but obviously I’ve already sewn the dolls wig onto the dolls head. Why didn’t I curl the hair before hand? Because I am a novice at rag doll making and was following a YouTube video. Please help, any tips would be great. Have a nice day!