@Ambiinii
If your Roku has been connected to a wireless connection previously, you can edit your current wireless settings in your router to match the previous. (SSID network name and password). Then you can use your Roku remote mobile app as your remote as the Roku should be able to connect. (remembers last known connection.)
If the Roku device has been factory reset, is brand new, or you cannot remember the last network's credentials (SSID network name and password), then you cannot use this method. You will need a Roku Remote.
Unfortunately, unlike the other Roku streaming devices and RokuTV, you cannot even just use a compatible universal streaming remote with IR. With the Roku Streaming Sticks, you will need a Roku Voice Remote as you need the RF (radio frequency wifi) to communicate with the device. After you setup with the new Voice Remote, you can then use mobile remote app.
You can purchase these Roku Voice Remotes in Walmart, Best Buy, Target, etc (about $20) if you need right away.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102