Operant has you aimed at the correct pins.
Measure the resistance to GND from those pins, then use a minimum 10 turn trimmer with a resistance ~15 times higher than the measured resistance.
If you measure 1kOhms, use a 15kOhm trimmer. If you have to, you can use a trimmer 10x the measured resistance, but be aware that this will increase the voltage significantly even when the trimmer is dialed to its highest resistance point.
Use the middle pin and one end pin, which end pin you use sets which direction will raise the voltage, lower resistance = higher voltage. Make ABSOLUTELY sure that the trimmer is set to the highest resistance between the two points you use before you turn the card on. Else, blammo.