How to get reference group form control D365 X++

 str  functionalid;

FormReferenceGroupControl control = this.design().controlName(formControlStr(EntAssetFunctionalLocationObjectInstall, FunctionalLocation)) as FormReferenceGroupControl;

 FormStringControl   subStringControl = control.controlNum(1) as FormStringControl; 

  functionalid = subStringControl.text();