Neily_
The app on your phone can only connect to a Roku that is already on your network so the app can't be used to configure a new network connection on the Roku. If you can set your WiFi router to use your former network's name (SSID) and password that your Roku knows to connect to, the Roku may connect when you then power it up. If not, you'll need a compatible physical remote to establish the Roku's network connection.
Is this really a Roku Stick? Some people erroneously call all Roku streamers "sticks". In the Roku world, this term is properly applied to any of several Roku "Streaming Stick" models. These have a male HDMI plug prutruding from one end, whereas non-Streaming Stick models have a female HDMI socket. This distinction is important because Streaming Stick models are designed to be used behind the TV set where infrared (IR) signals traditionally used by remote controls cannot reach, so they are controlled by WiFi, not IR. In the current Roku line, these are the Roku Voice Remote models and they are the only replacement remotes that can be used with Streaming Sticks, as to date no third parties have started supplying them.
All other Roku models have both wifi and IR receivers so they can be used with any Roku streaming device compatible remotes from Roku or third parties, including many universal IR remotes that have codes for Roku devices, and the above mentioned WiFi Voice Remotes. Just be sure you don't get a remote for Roku TVs (TVs with Roku capabilities built in) because Roku TVs use a different set of IR commands than separate Roku devices do.