Instructions for iOS
Step 1: On your device's home screen, locate and open the Settings app.
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Step 2: In Settings, scroll down and select Wi-Fi.
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Step 3: Find the network you're connected to and tap the i button (information icon) next to the network's name.
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Step 4: In the network information, scroll down and find Configure DNS. Tap on it.
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Step 5: Change the DNS option from Automatic to Manual. If there are already DNS servers listed, remove them by tapping the red minus button next to each server address.
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Step 6: Tap Add Server and enter the new DNS addresses. After entering the DNS server addresses, tap Save in the top-right corner of the screen. Also, to ensure the functioning of ICANN websites or conventional Web2 websites, you should also add DNS 134.195.4.2 to your configuration.
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Your DNS settings are now changed. Your device will use the new DNS servers when connected to the Wi-Fi network.