C# - MQTTnet library: how can subscriber can give (force) NACK on a packet (ApplicationMessageReceivedAsync)?

Question

I previously used RabbitMq and Kafka. Using Mqtt (Mosquitto) protocol V5 I would like to handle the negative ack manually. I expect these messages to arrive again on the next connection. I already handled clientSession and qos correctly (I'm already able to receive message on subscriber reconnection sent when the subscriber was offline, I'm using qos=2 exactly one). I checked https://github.com/dotnet/MQTTnet/blob/master/Samples/Client/Client_Subscribe_Samples.cs but it's not clear what parameters I have to set/use.

mqttClient.ApplicationMessageReceivedAsync += MqttClient_ApplicationMessageReceivedAsync;

        private Task MqttClient_ApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs arg)
        {
            //FIXME: TODO: manage ack
            log.Debug($"Received application message");

            OnReceivedMessage(arg);
            return Task.CompletedTask;
        }

in this function on arg I can set for example

arg.AutoAcknowledge = false;
arg.IsHandled = false;

or maybe I can not return a Task.CompletedTask.

So what's the right way to send to the server a negative ack with this library?

Thanks in advance for your cooperation.

Maybe I miss something or something doesn't work as I suppose.

Update If I set

arg.AutoAcknowledge = false;

the server resend message on reconnect, but it's the right way?