@priscillamoreno
If you have never setup/activated the Onn RokuTV with a Roku account (ie. setting it up to your network), you will need to do that with a physical remote before being able to use the Roku mobile app. You can purchase either a Roku Voice Remote or a universal streaming remote compatible with RokuTV. (Both of these can be found at Walmart, Best Buy, etc.)
If you have prevuiously setup/activated your RokuTV before losing the remote, you can try connecting your RokuTV via ethernet cable (if your TV is so equipped), and then try using the Roku mobile app to connect. Once connected, you can switch back to wifi.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102