I have an old Galaxy S6 that I would like to access again to retrieve some files. I can't remember the password so I want to use the remote unlocking feature. I am trying to use "Find My Mobile" but the site can't locate my phone for some reason. Location (GPS) is turned on and it is connected to my wifi. Does my Galaxy S6 need to connect to a cellular network for "find my phone" to work, or can it just be wifi?