Your Roku doesn't have an IP address until it's connected to your network, so don't bother with the app until then. The Roku 3 will work with any cheap universal remote that states that it supports Roku. They can be found at any big box store or sometimes at a dollar store. You might be able to use an Ethernet cable to get it to connect and then use the app, but I'm not sure it will automatically switch from using Wi-Fi to its Ethernet input.
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