@teemacs 

Hi,

I think the easiest way to connect a TP-Link range extender to an ordinary Wi-Fi router is to use the "WPS button" method.

https://www.youtube.com/watch?v=oCT-hAtL_IQ

  @woozle  Thank you, but my router doesn't have such a thing.

  @teemacs 

Ok. What is the model name of your router?

Usually routers that don't have a physical WPS button do still have a "virtual" WPS button within their user interface. (i.e. a button that you click on with the mouse)

It's one from our phone/internet provider here in Switzerland. Comes from a French company called Sagemcom. Sagemcom's models on its website have WPS buttons, but ours doesn't.

  @teemacs 

Is there no label stuck to any side (or the bottom) of the Sagemcom router that shows some name or numbers that indicate the model?

Have you'be been provided with login credentials for this router? (sometimes these are also printed on a label on the router)

Appears to have been a model specifically made for Swiss telecom company Sunrise. Ther instructions were plug in and switch on, using the password printed on the label on the base. And that was that, the way I like it, no need for a degree in computer science.

  @teemacs 

Provided I've found the correct user manual for the Sunrise router, WPS should be initiated via the "Wi-Fi" button on the top of the router. Apparently this is a three-function button.

The following is written in its user manual about the Wi-Fi button.

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- Short press (less than 5s) to enable/disable Wi-Fi function.
- Long press (more than 5s) to switch the Sunrise Internet Box to easy-pairing mode (WPS).
- Very long press (more than 10s) to initiate the Sunrise Internet Box easy-pairing mechanism over Wi-Fi with Sunrise TV Box.

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Therefore, to activate WPS on the Sunrise router you would need to press the Wi-Fi button longer than 5 seconds, but also shorter than 10 seconds.

Thank you! As they would say in my native Ireland, yer blood's worth bottlin'!  I had no idea that the wi-fi button did anything other than switch the wi-fi on and off. But then, I never did get a manual, just a card with instructions as to what to connect where, and this multi-functionality of this button doesn't feature. 

  @woozle Got it to work, so thank you! Nice that there exist folk such as yourself who are prepared to help technological Luddites.