So here is the Solution:

1. Make sure your iPhone 8 or iPhone 8 Plus is turned on.
2. open the 'Settings' app on your phone.
3. Choose 'WiFi' from the drop-down menu.
4. Select the 'Info' button next to the wireless network to which the iPhone is connected.
5. Choose 'Forget This Network' from the drop-down menu
6. see if this works.