How set scale limits of y-axis between 0-1 when values range from -9500 to 9200

I have a large data set of relflectance values

I am trying to change these values in order for the min value to be respect of 0 and max 1 i.e. -9500 = 0 and 9200 = 1

I've tried the rescale function different way but still get it scaled were all my values are between 0.508 and 0.512 rather than spread between 0 - 1

does anyone know why or have code that can help?

Thank you

Erin