One way to find symbolism and metaphor is to brainstorm words, images, or concepts that relate to your topic, theme, or message. You can use a mind map, a word list, or a free association technique to generate ideas. Then, you can look for patterns, contrasts, or similarities among them. For example, if you are writing about freedom, you can brainstorm words like bird, cage, flight, key, lock, escape, etc. Then, you can see how you can use them as symbols or metaphors in your story.
Another way to find symbolism and metaphor is to observe your surroundings, experiences, or emotions. You can use your senses, memory, or imagination to notice details, associations, or impressions that inspire you. For example, if you are writing about loneliness, you can observe how you feel when you are alone, what you see, hear, or touch, or what memories or fantasies come to your mind. Then, you can use them as symbols or metaphors in your story.