The very first thing is to wash your cat very very very very very well. Use a regular, non-medicated shampoo or Dawn dish soap, it does not have to be a pet specific product and time is of the essence, that is what matters most. After you wash your cat, like you’ve never washed before, don’t wait to take your cat to the veterinarian.
What is scary about dog products on cats is that they are very poisonous to cats and there is no antidote other than time and supportive care. Many untreated cats begin with shaking that turns into seizures and, unfortunately, this is often fatal. The sooner your veterinarian starts supportive care, the better the chance of flushing out the toxins.