I believe the crystal is connected in a series-resonant configuration,
which is less affected by circuit values. The only recourse may be to
purchase a new crystal.
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If crystal is indeed in series-resonant config. , by putting a trimmer of a
few pF in series with the crystal, it will highly likely be possible to pull
the freq 500 Hz.
After all this is only just over 4ppm of the nominal frequency.

Frank GM0CSZ / KN6WH