If your son has completed school, the 529 money can be distributed (at the owner's [Grandparent]) option) but the earnings will be taxed and a 10% penalty (for a non qualified distribution) added.
Another option is for the owner to change the beneficiary to another family member, typically the current beneficiary's younger siblings. First cousins are also eligible.
Reference: https://www.savingforcollege.com/article/how-to-transfer-529-plan-funds-to-a-sibling
