As far as I am aware, "श" is always pronounced as "sh" sound. Also, ष has the same sound as "श." स - s, सरल, सीमा श - sh, as in shoot, shirt... शीतल, शादी ष - sh, as in भाषा, हर्ष

धन्यवाद

The sound of श will be same as sh in "shirt" and Sound of स will be same as s in "sun"