In order to find the IP address your Roku is assigned to, go to Settings...Network...About [there you will see the IP address for Roku, and the Gateway(IP) for your router. These are actually LAN IPs or Network IPs. This is what you are concerned with when setting up the Roku. (192.168.1.xxx or the like) The IP you are seeing when you type in a browser "what is my IP" is something called a WAN IP. (this is what most people consider their IP Address.) That is the IP address assigned to you by your ISP to use the internet. (74.123.66.107 or the like)
As long as you haven't factory reset your device, you can try accessing your router and set your network SSID (network name) and password to your old ones, from your previous network. (if you can remember them). Your Roku3 is still trying to login with old creds, so you just change the router creds to match them.
There is another way using a hotspot(connect your roku3 to the hotspot ID) then you can go into your Roku Network Settings with the Roku mobile App and enter the new creds of your new modem settings. (set up a new connection). If you use your phone as the hotspot, you may need an additional mobile device to use the Roku mobile App. (ie a friends phone, or a tablet, etc) worst case scenario.
The final way is buy a universal streaming remote compatible with roku.
Once your Roku3 is set to your new network, can go back to using the Roku App as your remote.
See if any of the above helps you. Hotspot is probably an easy way to go if you cant remember your old login creds for your previous network. If you have factory reset the device, then remote is your only real option.
Hopefully one of these ways will work for you.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
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