The Lighting Controller

I’m sure that it’s a dummy question but I’ll go. If the button is big the speed slider inside is big enough to show the pourcentage and I’m able to slide it. When the button is small the slider is a line and I can’t (or I don’t know how) change it. How do I do?

When the button is too small, it is obviously not possible to use the slider.
It is not possible to change that.
The software displays a line to keep in mind there is a slider.