On the headrest there are two metal tubes that connect it to the backrest. Below the left one, there is a hidden button (feel it). It should feel like a (O) where there is a hole and a smaller diameter circle around it to give it a button feel. Press it while pushing the headrests up.
Didn't find this out until I read the manual, and I didn't have to before that because the headrest could tilt forward which is a good way to prevent whiplash in case of a rear-end.
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