I just downloaded "Infrared remote for roku" from the play store. It has a purple tv graphic. And it worked like a charm, other than of course having to be pointed straight at the device. I was able to then update my wireless network using it .
I too forgot my roku remote at home, but still felt confident that my Roku app would not fail me. Nope! Two hours later, searching the internet and trying everything, but nothing came close. Then, bam! Mobile Hotspot!....Please, please let me rename it...YES! Success.
If your phone has mobile hotspot, you are in luck. You can clone your home network. (if you don't know the exact name of your network, your phone does). Now you can use the moble roku app to control your roku to change the network settings to the new network. Turn off the hotspot. Reconnect your phone to the new network. Reload the Roku app.
My situation, Roku 3 went on vacation with me. Signed into the rental house wifi and all worked well. Upon leaving the rental I sadly left the remote. Once I returned home and hooked up Roku I realized the remote was no longer available, tried to bring up the iphone roku app but could not connect since the Roku 3 was looking for the wrong network (rental house). Finally, about to give up, I attached Roku 3 to ethernet on my router and did a hard reset. When it rebooted the iphone roku app worked and I could reconfigure Roku 3 to my network. Then I could connect to reset the wifi and all works fine. iphone app now is the remote for the bedroom Roku 3. Also serves as additional remote for living room Roku TV.