Extracting hazard ratio for subgroup from overall hazard ratio and hazard ratio of another subgroup?

Suppose in a clinical trial the overall HR of treatment A compared to treatment B is 0.66 (95% CI: 0.61 to 0.73). Now we stratify the treatment effect into two subgroups - based on a prognostic variable (subgroup C and subgroup C’). Suppose, in group C the treatment effect in terms of HR is 0.72 (95% CI: 0.51 to 0.79). Is there a way that I can calculate and extract the HR for subgroup C’?

Thank you very much in advance.