Networkable devices have no innate IP number. The IP is a net address that is assigned to the device by the network's router when the net connection is established, so until the Roku is actually connected to the net, it has no IP number.
This means you can't use the Roku app on a mobile device to connect the Roku to your net. The only way, as mentioned above, is via a compatible remote.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T