Easiest thing to do is find your IP Address on the router, which you can do by going to command prompt. Once you’re there type in ipconfigure which will give you a default gateway ip address. Type that IP into a new browser and login to router. Usually user is admin and then type whatever password you used when you set up router. Once you’re there you can change name and password to the Wi-Fi. You will need to change that to whatever the previous Wi-Fi network name was and password. Your fire stick will recognize the network name and should connect to your phone ( as long as that’s on the new network name. Works like a charm