I haven't tried doing this with the Kobo browser and don't know if it's possible, but obviously you need to change the "user agent" string that is a configuration string in every client browser. Here's an example talking about how you can change it in desktop browsers:
https://www.howtogeek.com/113439/how...ny-extensions/.
ETA: This discussion reminded me I had been wanting to do this on my Android tablet, where I run Firefox browser and a lot of the websites serve up content as if my 7" Nexus tablet is a larger tablet. Instead, I want them to serve pages to this tablet as if it's a mobile device. This
article described concisely how to go into the about
:config, add a custom configuration setting, and specify my own user agent. Found the user agent values for mobile
here, and it works great! Now if only it were that simple with Kobo's browser. Somehow, I'm guessing that it's not going to be. :-( Most browsers don't make things as user-configurable as Firefox, and even less so a dedicated device like a reader.
You might try raising this question in the Kobo developer subforum. I searched "user agent" there, and a only a handful of threads came up, like this one by davidfor:
https://www.mobileread.com/forums/sh...ght=user+agent