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.

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.

xcode证书管理出现这个错误解决方法：

简单点的直接按照Xcode的提示Revoke掉，然后新建证书，如果不想Revoke可以让拥有证书的人导出.P12文件，然后安装也可以解决，还有一种方法就是下面的方法：

1 点击Xcode，选择Preferences

2 选择 Accounts，如果没登录，就登陆自己的账号，然后双击团队的名字那一栏，就是红色框框那一栏

3 在弹出的界面左下角，点击+号，选iOS Development，就可以解决这问题了。