The 3810 is a Roku Stick, and will only work with an official Roku Voice Remote (there are several different models). You cannot use an IR remote of any kind (Roku brand or generic universal IR remote) because the Stick models (all of them) do not have an IR receiver. The only way to get a Stick connected to a network is with a Roku remote, as there's no way to use the app until a network connection has been accomplished.
Once you have your Stick connected to your home network, then the Roku app on a phone or tablet can be used to control the Roku, as long as it's a private home network (it won't work on a hotel or dorm type of network) and there's no WiFi security setting that blocks connected devices from seeing/communicating with other connected devices. That security is why the app won't work on a hotel/dorm network.
Your Stick will still connect to the last network is connected to, but it's likely you don't know the SSID and password of that previous network so you can't mimic it. Besides, if someone else was using that Roku, they either did a hard reset which wiped every personal setting from the Roku (at least they should have), or you're going to need to do the same thing to connect it to your own Roku user account. And once it's been wiped, you must have a remote to go through the initial setup from the beginning. No way around that.
Dan
Roku Community Streaming Expert
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