How to get the values for C1 and C2 in Chan-Vese Model?
The actual formulas are given on the publication, which I linked by editing your question. Besides, there are many publicly available implementations of Chan-Vese algorithm, including, but not limited to:

https://www.mathworks.com/matlabcentral/fileexchange/23445-chan-vese-active-contours-without-edges

https://github.com/kevin-keraudren/chanvese

http://www.ipol.im/pub/art/2012/g-cv/

https://www.mathworks.com/matlabcentral/fileexchange/19567-active-contour-segmentation

http://math.arizona.edu/~rcrandall/code.html

I think you could find all the details in those generously shared source codes.