@Solla-topee 

Hello, thank you very much for your support, but I'm afraid I still need some help as renaming the SSID is not the point.

Let's recap: 

1) I have a local Network whose SSID is, say, Vodafone1 (names are fictional).  All the devices wi-fi connected to this network thru a router, are automatically assigned an ip 192.168.1.x and all of them can navigate the internet. The only problem is that the devices located more distant from the router have a low signal. That's why I bought a TP-Link range extender

2) In order to set up the range extender (since the WPS method has not been succesfull) I used the manual configuration, so I disconnected one of my Windows 10 PC from Vodafone1 local network and I connected it to the LAN automatically created by the TP extender (say TPLINK1, still fictional). Of course this LAN at first is not connected to the Internet. So, following the quick start guide, I connected my PC to that Lan, then I logged in (admin / admin) to the Range Extender and set it up to connect do the Vodafone1 Lan. The setup has been succesful: checking the list of hardware connected to the Vodafone1 router I can see many devices, including the TP Link whose automatically assigned IP is 192.168.1.9

3) Since that moment the TPLINK1 LAN has disappeared, so I don't know how to login in to the range extender to edit the setup (still the TPLINK seems to be connected to the Internet but somehow "unreachable" by other devices)

4) Furthermore I have no idea if this effect is correct or if I should find a TPLINK1 network (which was available before the setup) to be used by devices which are located nearby the range extender or if they still have to be connected directly to the Vodafone1 network,