Hi @evabron,

When setting up the Range Extender, when you access http://tplinkrepeater.net for the first time, you will be asked to set a web management admin password for the extender.
If you have forgotten that password, the only way would be resetting the extender back to factory default and configure it again from scratch.
While it's powered on, please use a pin to press the reset button on the extender for 1 second to reset it back to factory default.