Next Step is finding the best DNS server for your Internet Service Provider(See: Selecting the Best DNS server for your ISP), Once you have found the best DNS server just Follow the steps below:-
Step 1: Connect the router and open https://192.168.1.1 from any browser. Log in as admin (By default username and password is admin & admin respectively)
Step 2: Go to Advanced Setup> DNS > DNS Server
Step 3: Select “Use the following static DNS IP address”
Step 4: Enter the Primary and secondary DNS server in these boxes.
Step 5: Click Apply/Save.
You have now successfully added a manual Domain Name System IP address to your router. Now start exploring the internet and check whether every site can be opened or not, if not change the DNS server again from the above method. If the problem persist change the DNS server to 18.104.22.168 and 22.214.171.124 these are the Official DNS server and almost every website can be opened.
*Click to Enlarge Images.