Since Tanzu Application Service (TAS) for VMs 2.6, you can only SSH onto the Ops Manager VM in a vSphere deployment with a private SSH key. You cannot SSH onto the Ops Manager VM with a password.
Note: If the private SSH key is lost, there is no way to recover it.
You have to generate a new pair of public/private SSH keys and replace the current ones. You can generate a new pair by referring to this Knowledge Base Article: Regenerate and install a new ssh key pair for the Ops Manager VM