Someone posted a new tool for helping with this the other day, it's on here somewhere. One option that I did though was to clone the card, then off move everything off the exfat partition to my pc, reformat it to a resizable fs (ie ntfs), then extend it to take up the unused space, and then convert it back to exfat and then everything back over
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Move all your files from the exfat to your PC, convert the partition to ntfs, extend it to take up the unused space, convert back to exfat, move files back