If your hair is very dry it's probably because you are using heat often and you may be using the wrong products. If you use heat often, wash your hair with a shampoo that has sulfates and then use other drying products like gels with drying alcohols then your hair won't be moisturized it will be dry.

I'd suggest changing to a more gentle shampoo and maybe try washing your hair less if you do wash your hair very often. Get some products that are non drying but still gives you hold and condition your hair a lot. Deep treatments are important for curly hair. You can also help combat the dryness by not using heat so often, you don't have to give it up forever but by learning what products to use for curly hair and developing a routine that works for you,you can have soft moisturized curls and you won't need to flat iron as much as you do.

There is a lot of information on here about curly hair products and routines. YouTube is also a great way to learn about curly hair.

Once your hair is heat damaged it can't be repaired, you can make it look better with certain products but the only way to really get rid of heat damage is to start taking better care of your new growth and slowly cutting off the damaged parts of hair. I'm not one of those people who believe you have to cut it off all at once if you can work with it until it starts to grow in healthy again but you can correct the damage in time.