You will want to replant some new seeds for your next crop. To do this, you need to remove the smart soil from the container (all the brown cork-like stuff) and rinse it in water to remove all seeds and plant matter.
Once you are satisfied that all plant matter has been removed from the medium, put it back in the pot and plant new seeds as if it were new!
**Note. It is encouraged to rinse the medium with boiling water to sterilise the growing medium before planting new seeds.
Alternatively, you could purchase new smart soil here.