public requires a certification process, I'm almost certain you don't want that.
Log into Roku site and go to "manage my channels", then "preview and update" the channel you're interested in. Near the top is a drop down menu that will default to "Preview and Publish" (next to another drop down that says "manage my channels")
Click on the "Preview and publish" drop down and choose the first option, "Properties", you will see a list of "Channel Stores" where you can click off regions where your channel should be allowed.
aspiring