The "Token Reactivate Notification Service" task periodically checks if DeviceID tokens are about to need reactivation will send out notification messages to the users if required.
The notifications that are sent are based on the parameters specified in the DeviceID policy setting parameters in the "Reactivate" section of the policy (see below);

The task can be found by navigating to "Administration | Tasks", then scrolling down to the task "Token Reactivate Notification Service";
The task parameters are used by the task script to determine which tokens are to be deleted and are edited by left clicking on the context menu of the task and selecting "Parameters";
A new window titled "Task Parameters" will now open that lists the parameters making them available for editing, and the default parameters for this task are as follows;

Select the parameter "application" then click the button, and a new window titled "Parameter - Edit" will open;
Specify the correct "application" that you are using for the Exchange ActiveSync by clicking on the down Arrow and selecting the correct Application from the list

Then click to update the parameter.

By default, the task is not enabled, but may be enabled by left clicking on the context menu of the task and selecting "Edit";
A new window will now open titled "Task - Edit";
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Select the "Enable Schedule" checkbox to ensure the task schedule is activated, then use the pencil icon ("") to specify the time and frequency settings for automated task execution.
The task can be run manually from the management console by left click on the context menu of the task, then selecting "Run";
A new window will open titled "Execute Task" will then open (the window will be populated with the default task property settings);

Ensure the parameter "Application" contains the correct name of the Application, and the name of the correct application that you are using for Excahange ActiveSync, then click the button.