The best fix is usually to avoid baking the problem in: use a truly neutral GND filter, or reshoot without it if possible. If you need to correct it afterward, work from the RAW file rather than a developed Photoshop image.

A RAW editor is the better tool here: use a graduated/local adjustment to independently correct the filtered area’s exposure and white balance so it matches the unfiltered area, while preserving highlight detail.

Editing after full conversion in Photoshop is harder because the RAW development step may already have applied tone/color changes. If you must do it in Photoshop or similar, a practical approach is to apply a gradual color and exposure correction with a mask/gradient, but matching the transition precisely can be tricky.

For the most accurate correction, you can shoot a neutral white target through the same filter/setup and use that as a reference to build a compensating gradient correction.

In short: RAW + graduated local adjustments is the preferred workflow; Photoshop-only correction is possible but less ideal.