How to Reset TP-Link Extender Password
TP-Link extender password reset process is not complicated. To reset the password, you just need to follow these steps:
1) Connect the extender to a computer using an Ethernet cable.
2) Open a web browser and type http://tplinkrepeater.net in the address bar.
3) Scroll down and click on “Forgot Password?”.
4) Enter your email address in the required field.
5) Enter your new password twice.
Source: https://www.wifiextenderhub.com/how-to-reset-tp-link-extender-password/