Adjust Nuvinci nfinity gears After the latest service, my manual Nuvinci nfinity is set to higher gear than before and I want it lowered again. Surfing the web I find nothing like "turn this knob to adjust gear".

The closest I find is installing and replacing it. There are two knobs, by the handle where I would suspect to find them, that might do the trick but they are not explicitly mentioned for after adjustment so I suspect they are only for tensioning the cable housing properly.  

Or is it unadjustable? Like when the end stops are set, it goes from 0% (lowest) to 100% (highest) and what has happened is that the end stops are not properly adjusted?
This would imply that the 0-100% gear at the rear is controlled by the 90% travel at the handle and one has to choose whether to have gears 0-90%, 5-95% or 10-100%.

(yes, I can ask the service person to do it but would prefer to do it myself. 
yes, I can ask the service person to teach me. but what would be the fun in that?)
So you are saying that the range of ratios available seems to have changed after servicing, so the lowest ratio available is higher than you want it it be?

I think you may be on the right track with the cable adjustment. The cable may be mis-adjusted so the hub is not at it's lowest ratio when the twist grip is at it's low limit position.

Loosening one cable tensioner and tightening the other should shift the relative position of the twist grip and hub mechanism. Keep track of how many turns you apply so you can get back to where you were if you find you are adjusting it the wrong way.

Link to service manual for the hub: https://www.gazelle.nl/media/gene-cms/h/a/handleiding_nuvinci_nfinity_1.pdf