Here's what has worked for me to re-establish my net connection. I usually have to do this on my most used Roku, a Streaming Stick+, several times a month.
Restart your router (even if other devices have no problem finding and connecting). Sometimes that's all it takes, if not keep going.
Restart the Roku to clear its memory via Settings > System > System restart (for Roku TV it's Settings > System > Power > System restart). Again sometimes that's all it takes, if not keep going.
Find and connect to your network via Settings> Network > Set up connection
If that doesn't fix it, try disconnecting the power to your Roku for a few seconds. When it comes back up, see if you then can set up the network connection.
Roku Community Streaming Expert I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well. If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X