Ruining 1100A strimmer Unable to remove head?

Ryobi 1100A ELT line strummer
Unable to remove head ? Damaged thread

Issue with with the head assembly to change the line. I can't get it unscrewed, it just "spins" loose, does not seem to be unscrewing from anything

Bunning still sells extra heads -- https://www.bunnings.co.nz/ryobi-line-trimmer-accessory-line-head-elt-plt_p00510075
but even if the head WAS a problem because of age or similar, how the HECK do I change it if I cant get it off?