How do I do that?
Unfortunately, using Alexa as an external speaker is only supported when using Amazon Fire products, not using a Roku. To set that up, you will need an Amazon Fire Stick or Fire Cube. Once you have that, you can follow the directions from Amazon here.
However, there are some things you can do to control your Roku using Alexa – just not as a speaker for your television. You can read more about that on Roku’s blog.