Quill mites you will need Ivermec which is obtained from your vet ...
Birds can loose their feathers like that from stress related illnesses
Ie: Mites , Quill mites, FM and moulting ....
I am looking at the feather that fell out and like i have said to others I am not a "VET"
but the quill end on a FM bird "usually" has a broken end - When i had issues
that was the first sign the vets told me it a dead give away ....
again contact local avian vet for a test - It looks like a premature feather that as fallen out due to the blood which is still in the shaft of the feather which is a sign of quill mites it you look closely at the feather some say that you can see tiny holes in the shaft where the motes have borrowed into it There does seem to be stress marks on the feather from what I can see on that photo.
again I am not an EXPERT