iOS | How to transfer call

In android docs stay how to transfer call even from outgoing state. I don't know how to do it for iOS.

I have this code to start new outgoing call which then I want to transfer to the call which become held after new call is initialized.

func transferCall(contact: Contact, completion: @escaping(Error?) -> Void) {

        

        if let contact = contact as? RainbowContact {

            servicesManager.rtcService.startOutgoingP2PCall(to: contact, withFeatures: .audio)

            

        } else if let number = contact.phoneNumbers.first?.number, let phoneNumber = PhoneNumber(phoneNumber: number) {

            servicesManager.telephonyService?.makeCall(to: phoneNumber, fallBackHandler: { _, _ in }, completionHandler: { err, number in

                if let err {

                    completion(err)

                    return

                }

            })

        }

    }