Don't worry about extender login, It is so simple: 

Connect your extender to the router using the WAN port. 

Insert an ethernet cable end into the extender port and another to the computer. 

Open any web browser on the same computer and type ap.setup in the address bar. 

It will take you to the administration login portal, After login can make changes and set up without any issues. 

If you are getting any kind of issue can get connected to officials. 

To get instant solutions to common problems reset your extender. just hold and press the reset button for 10 seconds. Your extender will reset shortly and you will be able to make changes as per your need after login.