在配置管理器中，您可以为您的项目添加一个新平台.但是，如果您已经为您的解决方案添加了平台，您需要取消选中创建新的解决方案平台"，否则您确实会收到解决方案平台已经存在的警告.

In the configuration Manager, you can add a new platform for your project. However, you need to uncheck the "Create new solution platforms" if you already added the platform for your solution, otherwise you will indeed get the warning that the solution platform is already there.