I would look in the ear first, no need to jump on drops - the symptoms he is exhibiting in the video is pretty clear that it's very likely Wry Neck, but I wanted to mention ear infection "just in case".I have ear drops that I use for my dog , miniature schnauzer, for when she had a ear infection. If he does have a ear infection do you think I could put a drop of that in his ear?
I don't know what type of drops you have. IF, IF there is ear infection - that can be caused by a number of things - from ear mites to respiratory disease. General care for ear infection in chickens is to apply 1-2 drops Peroxide in the ear to help bubble out debris, remove any pus/gunk, etc. that you see and pack the ear with triple antibiotic ointment. Repeat daily until it clears up. Depending on the cause antibiotics may be needed to help clear up infection.