That long essay regarding failure to understand a philosophy exam helped me to feel better. This activity felt like I was caring for myself. Instead of letting my emotions rage, or trying to bury them, I worked them out in writing.
Your soul is not some mysterious thing. It is the entity that lives here in you, with all its various levels of awareness.
Taking the time to process your emotions. Taking the time to listen inwardly. Taking the time to reason things out. Taking the time to become aware of yourself, who you really are. These are examples of taking care of your soul.
It seems to me, at times, that my whole job here on earth is caring for my soul. All my relationships enhance and expand this activity. So caring for my soul must be a relationship with my soul. Does it help to call my soul my inner being? That being which is quieter than my emotional thoughts? Become aware of that quieter presence inside. It helps a lot to pay attention to it.