I have a Roku TCL model 32S335 (32"). After reading all of the troubleshooting tips on the entire WWW, I found a simple solution:
1.) The ROKU mobile app will NOT find or pair to your TV if it is already turned on.
2.) Do NOT try to use the "Connect Remote" settings in the TV.
3.) Simply UNPLUG (not just turn off using the remote) but UNPLUG the TV.
4.) Open the Roku App on your phone and then click the "Devices" icon in the lower right corner.
5.) Immediately, plug the TV back in and power it on.
6.) The app will now detect your TV and you're DONE!!!
Tony from Baltimore, Hope this helps.