If your Roku Streaming Stick remote is no longer working, you will likely need to purchase a replacement remote, as you will only be able to connect to the mobile app if the device is connected to your network.
Can you please let us know which Roku Streaming Stick you have so we can make the appropriate remote replacement recommendation?
My Roku remote won’t work and because I got a new modem my phone app and streaming stick won’t work because I can’t connect to it to change the network settings
As @RokuDanny-R mentioned, you can't connect a Roku Stick to a network without a working remote. What you can try is changing the wireless name (SSID) to match your old network name, and use the same password. As long as the Stick hasn't been reset, it should re-connect if it's the last network it was successfully connected to.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), 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.