How to downgrade vSphere ESXi 6.0 license keys

I'm trying to downgrade vSphere ESXi 6.0 license keys to VMware vSphere ESXi 5.5

I see the following:

https://kb.vmware.com/s/article/2006975

How to downgrade license keys in My VMware (2006975)

However,  I don't see Manage License Keys from the navigation bar.

It's difficult to navigate around myVMware. I did find:

Manage License Keys– View and manage license keys by product or folder.

But it's a dead link.

https://my.vmware.com/group/vmware/my-licenses

How can I easily downgrade my vSphere 6 license to vSpere 5.5?

Any help would be appreciated.

Thanks