You can reset the router and just restart the TV. You can also go to WiFi settings and forget about the network. Once that is done, you will need to search for WiFi and reset it. You can find the options in the menu itself.
Or you can reset the Vizio TV to factory settings. But be careful to do this, cauze you will lose all settings on the TV.
First you should check if there is a problem with your wireless network. If the internet signal is weak, Vizio TV will keep disconnecting. , you can connect another device to the same network and use it to access the Internet to see if it works.