Do this from with the esxi host web client, you should be able to go to the ip that shows up on the main screen for vmnic . If you logon by going to that ip in the webbrowser you can use root and the correct password to logon. Click on networking and the vmkernal nics.
if you want to do it from the console you need to enable tech support mode
ESXi Tech Support Mode | Arnim van Lieshout
then from the console esxicli commands to get the ip
esxcli network ip interface ipv4 get