If the neem infused oil got too hot and burnt the neem, it's recommended that you avoid using it on your hair. When neem leaves are overheated, they can lose their beneficial properties, and the resulting oil may be less effective or even harmful for your hair and scalp.
Using burnt neem oil on your hair could cause scalp irritation, dryness, or other issues, so it's best to err on the side of caution and discard the oil. Instead, consider making a fresh batch of neem infused oil using a lower heat setting or using a double boiler method to prevent overheating.
If you don't have access to fresh neem leaves or the time to make your own infused oil, you can also look for commercially available neem oil or hair care products that contain neem oil as an ingredient. However, be sure to read the labels carefully and choose products that are free from harmful chemicals and additives that may cause further damage to your hair or scalp.