ok, nintendo switch is out of league, since i am not familiar with this device and how the connection progress works with the game. changing the ip should not be needed, you can find out the IP of your device given by your router in "settings", "internet" and thats what you should use manually on the client to connect to your host. seems you could already find the game, if it's done automaticly or via a join code, that might cause problems. if manually connect however leads to the same problem, it most likely sounds like your wifi or router settings are to blame. probably try this in another environment first (wifi of your neighbours or an old unused router).
did it work before? i think someone else should step in to help.