You can create EKRecurrenceRule object from iCalendar fromat.
let recurrenceRule = EKRecurrenceRule.recurrenceRuleFromString("RRULE FREQ=MONTHLY;INTERVAL=1;BYMONTHDAY=13;BYDAY=FR")
let recurrenceRule = EKRecurrenceRule.recurrenceRuleFromString("RRULE FREQ=MONTHLY;INTERVAL=1;BYMONTHDAY=13;BYDAY=FR")
print(recurrenceRule?.stringForICalendar())
// => RRULE FREQ=MONTHLY;INTERVAL=1;BYMONTHDAY=13;BYDAY=FR