How to convert Z level to sigma level

Hi everybody,
I am new to use cdo.
I have download salinity and temperature at Z level (Z= 37 ) with 1/12 degree resolution, but I need to convert them to sigma level(=20) with 1/30 resolution.
I attached the file, I really need to do it , My work has stopped because of this problem.
I would be grateful if you could guide me.
I am looking for any suggestions,
Thank you in advance,

Best
Pooran