Hello, i need help on what have to do for "reset" the notifications of new incoming devices to my network

In Teether app,I've deleted the Offline Client from that list, then i've tried test reconnecting the device in my wifi or wired lan, and the notification of "new device connected" does not appear, it gets listed as a normal already registered device,even it keeps its name.. 

My questions are:

1.- What's the point of the "Delete offline device(s)" option ??  

2.- What have i to do to delete or reset the "registry" of a device in the app? the idea is that when it gets connected again to my wifi, the app notification appears again.

Thanks...