These instructions are specific to the vSphere 6.5 vCenter installation. Here are the steps to install PSC on an existing Windows 2012 R2 server:

1. Download VMware vCenter server and modules for the Windows ISO file from: http://www.vmware.com/download.
2. Mount the ISO file once it is downloaded.
3. Launch the Autorun application in the root folder.
4. Click on vCenter server for Windows and then the Install button.
5. Click on Next.
6. Accept EULA, then click Next.
7. For the deployment type, click on Platform Services Controller under External Deployment:

8. Verify the system name and click Next.
9. Choose your SSO domain name, user, and password. Click on Next.
10. Change the default ports if needed. Click on Next.
11. Change the destination directory if needed. Click on Next.
12. Choose whether to join CEIP or not and click Next.
13. Review the settings and click on Install.
14. When the installation is done, click Finish.