You haven’t given enough information to pose a reasonable answer… what have you done with the ESXi hosts to send logs? What have you set up in Graylog to receive logs… We can help with your work if you show what you have done and have a particular point where you are stuck…
Here are some tips on how to make your question clearer here and here.
Thank you so much for your response. The issue has been resolved post reboot of ESXi hosts.
Also, based shared link we have configured the syslog in ESXi.