$vmName='TESTVM'
function enableCpuCompatibility($vmName){
    $compatibilityForMigration=(Get-VMProcessor $vmName).CompatibilityForMigrationEnabled
    if(!$compatibilityForMigration){    
        $vmIsRunning=(get-vm $vmname).State -eq 'Running'
        if($vmIsRunning){stop-vm $vmName}
        Set-VMProcessor$vmName -CompatibilityForMigrationEnabled 1
        if($vmIsRunning){start-vm $vmName}
    }else{
        write-host "$vmName already has CPU CompatibilityForMigrationEnabled set to True"
    }
}

enableCpuCompatibility $vmName