This is how to change your VMware vSphere ESXi SNMP settings with PowerCLi.
# Connect to your ESXi server
Connect-VIServer -Server <servername> -Protocol https -user <user> (-password <password>)
# Check current SNMP settings
Get-VMHostSnmp
# Set the SNMP community string + enable SNMP
Get-VMHostSnmp | Set-VMHostSnmp -ReadOnlyCommunity ‘string’ -Enabled:$true