There are two ways to enable SSH to allow you to putty onto a host.
1) Enable physically by visiting the esx/esxi host.
2) I am going to explain how to enable via the vsphere client incase you can’t get to host due to it being at a remote site, and you don’t have ilo access.
1) Firstly, access vsphere
2) Click your esx/esxi host
3) Click the configuration tab
4) Click Security Profile, located under the software box
5) Click properties located towards the right
6) Locate Remote Tech Support (SSH) and click. Status should be stopped by default. See screen shot below.