handle on swan chair  

Simon
The swan chairs used to be available with tilt function (which makes them much more comfortable) and the hole you see is to adjust the tension on the tilt. However, unlike the egg chair with tilt, the swan chair just has a hole where you can insert an allen wrench to tighten or loosen the tension. There is no visible handle on the exterior.

Thanks
Pegborad, Will have a look and see if I can access it.

I've had a tilting version...
I've had a tilting version that looks like this....Never knew it could be adjusted

jesgord
Is the upholstery original? It's not uncommon for them to be reupholstered and the hole to be covered up.
I have a pair that I had redone in cognac leather. The shop did not make a hole in the new upholstery, but I know where the opening belongs (you can feel it if you run your fingertips over that area) and I'm happy with the tension on the tilt, so I figured I'd leave it as it is.

Ok so the trick question
Is how to free up a mechanism which has ceized????

Yikes!
So did you get an allen wrench into the fitting? It won't budge?
I guess I'd try a bit of WD40 or comparable lubricant, taking care not to soil the upholstery if it is in good shape of course.
If it can't be adjusted, is the tension too high or too low? Can you live with the amount of tension or tilt as it is?
I don't know how you might fix it as it is inside the foam structure and to get to the mechanism you'd have to strip the chair of it's upholstery and foam and probably cut into the foam.
Good luck.

It budged but
Was tighter than my dads wallet and still the chair does not tilt. May need to soften it with some wd40 if it has been unused for years.
I dare not force it as i dont fancy breaking the back!