How to forget a Wi-Fi network on your iPhone, iPad, or iPod touch

Forget a network on your iPhone or iPad

1. Go to Settings > Wi-Fi.
   
2. Tap next to the Wi-Fi network that you want your device to forget. (SDIRC_BYOD or Guest Wireless)
   
3. Tap Forget This Network, then tap Forget to confirm.
   

https://support.apple.com/en-us/HT208941