Unity - Mobile - How to access to camera fields?

Using Vuforia 7.5.26, Unity 2018.2.5f1 and building on Samsung Galaxy S8+, Android v8.0.0. I need to adjust the "exposure-compensation" field.

This "for" loop doesn't output anything.

foreach (var f in CameraDevice.Instance.GetCameraFields()) {     Debug.Log("key; " + f.Key); }

I also tried  CameraDevice.Instance.SetField("exposure-compensation", -2);

CameraDevice.Instance.SetField("exposure-compensation", "-2");

It also tested with a Nexus 5. This time, it can iterate through all fields but setting the exposure field doesn't change a single thing.

My main issue here is that using Vuforia, I must look at a LED. If I take a picture using my phone, the LED color is perfectly fine. When Vuforia is running and I access to the camera image, the LED looks oversaturated, almost white. I want to lower the exposure-compensation field. I'm also wondering why the image is so bad when using Vuforia. (My camera device mode is set to QUALITY in the vuforia configuration). Please help me! Thanks