The plastic gauge will come off, it just 'snaps' into place and then a socket could be used... BUT.... if you tighten the gauge, you risk creating a larger leak, messing up the gauge accuracy or damaging the gauge mechanism.
You can only lower the vapor pressure by cooling the tank to 'freezing' temperatures or by draining the tank empty. I do not recommend either way, you need to take it to a qualified propane dealer and they will do it correctly.
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