Just did this 3 weeks ago
1, you need all your paper work from your country done,sealed, and ect.
2. You go to animal office at the airport i think next to luggage 2
3. You pay the 500 baht
4 then you go to customers declare your animal and they will give you a tax based on age. Mine was
*****
for 3 dogs. They not care if service,emotional or pet
If you leave the country and return with the pet you fo not have to pay it again.
Hope that helped