Your account already has a signing certificate for this machine but it is not present in your keychain. To create a new one, you must first revoke the existing certificate.
Youraccountalreadyhasasigningcertificateforthismachinebutitisnotpresentinyourkeychain.Tocreateanewone,youmustfirstrevoketheexistingcertificate.xcode证书管理出现这个错误解决方法