Any rings on Speedboosters from Metabones are to adjust aperture of (like the Name of the Adapter Implies...) G-Style Nikon F-Mount Lenses, which do not have a Dedicated Aperture Ring, and rely on the Adapter or the Camera to Set the Aperture.
To adjust the Focus of a Speedbooster, there is usually a small Screw somewhere near the Camera Side of the Adapter (MFT-Mount), which can be loosened to adjust the Optical element in the Speedbooster, at least for the Nikon-Versions of the Speedboosters.
This Adjustment is however only recommended if you actually need to do that, and know what you are doing. Other Focus Adjustment on the Speedboosters is not Intended By Design.
To learn more about G-Style Nikon Lenses, see:
(under
G- )
https://en.wikipedia.org/wiki/Nikon_F-mount#Electromechanical_and_data_communication