iPhone
Option 1 — Toggle Airplane mode
Toggling Airplane mode on and off is the simplest approach.
Open the ‘Settings’ menu.
You will notice an airplane icon. Toggle this on by clicking it.
Toggle it off by clicking it once more.
Option 2 — Reboot your device
Rebooting should clear your DNS as well.
Option 3 — Dump Network settings
This will clean your cache, but it will also stop your Wi-Fi connection for a short time.
Open the ‘Settings’ menu.
Select ‘General’ from the drop-down menu.
Reset the network settings by clicking ‘Reset’, then ‘Reset Network Settings’.
After that, your device will be rebooted. You must manually reset your DNS servers if you already modified them.
Android (8.0 Oreo)
Flush DNS cache
Launch Chrome.
Type chrome:/net-internals/#dns into the address bar.
Click ‘DNS’ in the left pane.
Click Clear host cache in the right pane.