How to slowly decrease saturation as the player takes damage?

I don't know how to manipulate the Grayscale image effect to slowly fade in as the player takes damage

Here is a code I got from a friend I just need to modify it. This script will activate when the player's exosuit is in critical condition so the player will begin taking damage.

Code (CSharp):

1. using UnityEngine;
2.  
3. public class ExoCritical : MonoBehaviour
4. {
5. public int maxHealth = 100;
6. public int currentHealth = maxHealth;
7.  
8. public void TakeHit(int amount) { currentHealth -= amount;
9. If (currentHealth <= 20)
10. {
11. //Saturation fade out start
12. }
13. If (currentHealth <= 10)
14. {
15. //Noise filter activate
16. }
17.  
18. if (currentHealth <= 0)
19. {
20. currentHealth = 0;
21. //Display text KIA
22. }
23. }
24. }

 

https://www.assetstore.unity3d.com/en/#!/content/83912
Download this to set your preferences for the post processing effects,
when you have different prefered settings, change the current one used in the camera when the player takes damage