I was apply patch on Dynamics AX 2012 R3. During update checklist process. I found, Code merge check box was disabled. Message described that we need Team Explorer for Microsoft Visual Studio 2012 to enable it.
Microsoft Official download link was not working. I downloaded it from here, And it works for me.
Remember, the above link is unauthenticated and third party, download it on your own risk. But some how the other we need to download it.