If you are not seeing the option to terminate the call while viewing the Queue List component, this could be happening due to two potential reasons:
Your Natterbox user does not have the permission level set as Team lead or Admin. See this guide for how to resolve.
The wallboard is not configured to allow call back termination. This is how you can amend that:
Navigate to the wallboard in question, then click edit.
Edit the Agent list component.
In the component please ensure that "Can terminate calls " is ticked

Press Save within the component as shown in the above picture.
Press Save under the Wallboard page (as shown in the picture below) to implement the changes to the Wallboard.

f. To access the option, simply click on the Settings cog icon, and Terminate call should now be available for active calls, as shown in the picture below. Please note: This option is also available for callback calls waiting in the queue.

Once you have applied these changes, you can perform a test call towards the call queue in question and request a callback, then navigate to the wallboards and perform the termination action.