@Maddy1010 

If you are talking about the wireless password of the TP-Link device, please check the default password on the device label. You can login to its web interface page to find it if you changed it to your own. Here is the guide you can refer to:

https://www.tp-link.com/support/faq/399/

However, if you are talking about the login password, which should be admin by default. If you changed it and don't remember, you need to reset the TP-Link device to factory defaults, then you can login again by admin and create your own again:

https://www.tp-link.com/support/faq/73/