Begin with a sentence that uses this form:
Where there was once …., now there is …..
You can write about something tangible that has changed right there in front of you. You can write about the invisible shifting ideas in your imagination.
What used to be different? The weather, your food preferences, the geraniums, your attitude, your spine?
What has come into being? A person, a garden, a notion, a friendship, artwork?
What no longer exists in its old form? A shirt, a pet, the carpet, a memory, a vehicle?
Since everything changes, you can write about anything at all. Tell how it used to be and what it is like now.
When you have finished, give your work a title. Write the date on it, too. Add a drawing or other decoration to the page if you like.