Palette,Corgi,does it once in 2-3 months or so.
I be calm,and with one left hand,I put the head looking up and with my left fingers,I cover the nose hole. Then, with my right hand,I rub the throat slowly.
This usually stops the reverse sneezing in 3 seconds or so. I cover the nose hole because that makes your dog to be able to breathe from mouth.
When sneezing happen,Palette come closer to me because she probably knows mommy can help and stops right away.