Why can't I attach spring arm to character head?

I shift the camera to the start point of the spring arm so that I also have a first person perspective, the problem with this is that it because the character’s head moves forward slightly it really needs to be parented by the head in order for the view to be stable.
Please see attached, where I can’t select anything under ‘parent’
Any help would be welcome! Thanks!

You need to attach the boom or the camera directly to the skeletal mesh.

Then make sure your mesh has a head socket in the right place.

Finally select that as the socket for the attachment

Thank you! It worked.