Hi there, friend!
Solution 1
You can reset the DNS service
1. In most cases, the default user name for logging in to the web page is root, the password is admin, and the IP address is 192.168.100.1. However, for security reasons, the default password or IP address may have been changed before delivery. The nameplate prevails. Enter the IP address in the address bar of your browser.
2. Enter the default login account and password on the nameplate on the rear of the ONT, and click Login.
3. Click the Network Application tab and then choose DNS Configuration from the navigation tree. In the right pane, configure DNS template, DNS parameters, and you can also configure static DNS domain name resolution.

4. Click Apply.
Restart your router and computer to make sure you can access the Internet
Solution 2
If the fault persists, restore all configurations before the fault occurred.
If you haven't backed up your configuration data, contact your ISP and ask them to configure it remotely for you.