You can already control Roku with the corresponding remote control or the Google Assistant via voice control. But if you have an echo, you were out of luck. A new Roku skill changes that by putting Alexa voice control on your devices.
Roku is the best streaming device for the person who wants to see everything. With Roku, you can watch movies and TV shows from almost any store, whether Amazon, Google, Netflix or your favorite channels like CBS, NBC or PBS. It has an easy-to-use interface and even offers 4K support at pretty low prices.
However, if you want to control your Roku with your voice, you'll need either a Roku remote with a built-in microphone or a Google assistant. Everyone in the Alexa camp was excluded. Now Roku addresses this with a new Alexa ability. After installing the skill, you can control any Roku device or TV with Roku OS 8.2 or higher. You can start movies and apps, and if your TV has Roku, you can even control features like volume or switching inputs.
Similar to Google Assistant, voice commands must use Roku as their name, ie Roku should open or open Hulu Open Hulu on Roku. And unfortunately you can not control Netflix with voice commands.
Setting Up the Roku Alexa Ability
When starting, only other Alexa abilities are installed. Open the Alexa app and tap the Hamburger menu in the upper left corner.
Touch Skills & Games.
Tap the magnifying glass in the upper right corner and look for Roku.
Select the Roku option from the results. 
Tap "Enable to use".
Enter your Roku credentials, tap the "I am not a robot" box, and then tap "Log In"]
Tap the Accept and Continue button ".
Select the Roku devices for which you want to enable Alexa control and tap the "Continue to Alexa App" button. 
You should receive a message linking Roku. Just tap the X to return to the Alexa app.
Remember To Say Roku
When you're done, you can now control your Roku devices from Alexa. Remember that you have to say for the voice commands as part of the Roku command. But now you can say "Showtime on Roku Launch" or "Show Action Movies on Roku" and so on. As always, Alexa works best when you group your devices. So you should add Roku to the group with the next echo.