Connect to the router and open the url http://tplinklogin.net/
Enter username and password. Now navigate to Lan Settings under Network and change the IP address of the router that is different from the main router.
Save the changes, wait till the router restarts with new IP.
After the router restarts navigate to wireless security, click on enable WDS briddging. Select channel from main router. To get this information click survey, discover your main router and connect to it. Enter the password of the main router and while you are here note the channel of the main router and enter it in WDS bridging settings under label channel.
Router might restart here, then navigate to wireless security and set password for your 2nd router.
Also click on DHCP and disable DHCP.
Click reboot. Now you will notice that your second router acts as your wifi booster.