It depends on the model Roku you have. If it's a Roku Stick of any kind, you can only control it with a genuine Roku WiFi Direct remote. And the same remote doesn't work on all Stick models. If it is any other model of Roku player, i.e. anything but a Stick, then you can use a generic IR remote that can be purchased almost anywhere. Just make sure the packaging lists Roku players as a supported device.
There is one other potential workaround. If you can log into the new Internet router and have the proper permissions within the configuration, you can change the SSID and password for the WiFi to match your previous router. But both must be identical to the previous router. And don't perform a factory reset on your Roku or you are truly stuck without an actual remote.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
Yes, @Tnjensen10, I had followed exactly what you did! My controller just died one day.
New batteries 3 times, unplug stick, plug back in multiple time, etc. My biggest mistake was to follow the instructions in the troubleshooting guide that said to hit the reset button... big mistake! It rendered my $35 streaming stick completely useless without buying a new $20 remote. If I would not have hit reset, I would have at least been able to use my phone as the remote through the app, which would have been fine with me.
They just cannot give us a straight answer!! I moved. Roku says "Not connected" I'm unable to use phone or remote to get Roku to settings so that I can set up wireless. We KNOW HOW to set it up, but we need to be able to manipulate the menu!?