When you have the enough ingredients, the Create button will be green, tap on your Aquapedia. The first species you see will be for the event.
You tap on its icon and then tap create.
A fish egg will pop into place on your reef.
If you tap the egg you can see how long it will take before it’s ready to hatch.
Once your egg is ready to hatch a flashing circle will appear around the egg, tap this to hatch your first event species! You can speed up the egg using Splashcash.