To fix, or rather regain the ability to feel again, it's important to be gentle with yourself. Try reconnecting with your body, practicing deep breathing, doing some catharsis, journaling, and creating a safe environment for yourself. Seeking out professional support is usually crucial, as emotional numbness is usually a major sign of a traumatized nervous system. To regulate your nervous system, you need a safe holding environment, which a professional therapist/counselor can provide.