Maybe it´s easier to look at this figure:
Dateianhang:
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E-M-PIC_0071.JPG [ 10886-mal betrachtet ]
Move the aluminium tongue (blue point) to change the voltage. But be careful this aluminium tongue breaks easily.
In your case it is more recommended to insert a narrow paper sheet like red arrow shows. Doing so the voltage will increase.
Watch the effect by your DVM and insert as many sheets until the voltage will have been climbed up on the desired value.
Be patient the voltage jumps often too high or too low.
But note: There are a few other reasons for loo low voltage at battery terms. Check all cable connectors between regulator,
ignition switch in the lamp, fuses and battery. Often the main switch or the fuses are responsible for a non-acceptable voltage drop.
Also note that the nominal voltage at battery terminals is 6,8V ... 7,0V at about 3000min-1 and full light (6,3V is too less).
Regards
Lothar