Can you please provide us with more information regarding the issue you are experiencing? Have you tried restarting your Router? Is there any error message when trying to connect? Did you try to connect the device to your home network or to the router?
Furthermore, if the affected device is either a Roku Express or Roku Premiere, please note that they are only compatible with wireless b/g/n networks on the 2.4 GHz spectrum. Ensure that your hotspot is broadcasting a 2.4GHz Wi-Fi network for the device to connect to. You can check your device model by navigating to Settings > System > About. If you are getting an error code or message, refer to this link for common Roku error codes and their recommended actions: How to connect your Roku device to the internet using Wi-Fi or Ethernet.