Here is what the dealer told me, if you have the up/down button for the headrests then it's fully automated. There is no other release, hold up button for 8+ seconds to reset.
I have this setup and my headrests were stuck in the up position. I took the seat and trunk apart and found nothing to reset. The problem was a bad valve, it's all hydraulic. The cost for parts and labor was $1000. I hope your issue is not as bad but the reality is that you will probably end up paying for at least a diagnostic.