1 - Disable the enrollment group
2 - delete each device from the identity registry.
3 - Delete the enrollment group.
Reference:
https://docs.microsoft.com/en-us/azure/iot-dps/how-to-unprovision-devices

The Device Provisioning Service supports the following forms of attestation:
Reference:
https://docs.microsoft.com/en-us/azure/iot-dps/concepts-service#attestation-mechanism

You may find it necessary to deprovision devices that were previously auto-provisioned through the Device Provisioning Service.
In general, deprovisioning a device involves two steps:
1. Disenroll the device from your provisioning service, to prevent future auto-provisioning. Depending on whether you want to revoke access temporarily or permanently, you may want to either disable or delete an enrollment entry.
2. Deregister the device from your IoT Hub, to prevent future communications and data transfer. Again, you can temporarily disable or permanently delete the device's entry in the identity registry for the IoT Hub where it was provisioned.
Reference:
https://docs.microsoft.com/bs-latn-ba/azure/iot-dps/how-to-unprovision-devices

The IoT Hub resource logs connections category emits operations and errors having to do with device connections. The following screenshot shows a diagnostic setting to route these logs to a Log Analytics workspace:

Note: Azure Monitor: Route connection events to logs:
IoT hub continuously emits resource logs for several categories of operations. To collect this log data, though, you need to create a diagnostic setting to route it to a destination where it can be analyzed or archived. One such destination is Azure Monitor Logs via a Log Analytics workspace, where you can analyze the data using Kusto queries.
Reference:
https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-troubleshoot-connectivity

Devices use telemetry to send numerical data from the device. A rule triggers when the selected telemetry crosses a specified threshold.
E: To create a telemetry rule, the device template must include at least one telemetry value. The rule monitors the temperature reported by the device and sends an email when it falls below 400 degrees.
B: Configure the rule conditions.
Conditions define the criteria that the rule monitors. In this tutorial, you configure the rule to fire when the temperature exceeds 70°F.
1. Select Temperature in the Telemetry dropdown.
2. Next, choose Is less than as the Operator and enter 400 as the Value.

3. Optionally, you can set a Time aggregation. When you select a time aggregation, you must also select an aggregation type, such as average or sum from the aggregation drop-down.
Without aggregation, the rule triggers for each telemetry data point that meets the condition.
With aggregation, the rule triggers if the aggregate value of the telemetry data points in the time window meets the condition.
Reference:
https://docs.microsoft.com/en-us/azure/iot-central/core/tutorial-create-telemetry-rules