Hi Svetlana !
I can only give few tips ( as I transferred my dog FROM Seychelles to Malaysia.)
-Make sure your dogs vaccinations are up to date.
-Microchip required
Rabbies vaccination is necessary , as Seychelles is rabbies free country .
Go to government or authorised VET in Bulgaria to prepare your dog veterinary health certificate .Basically it is a paper that your dog is fit to travel.
Than contact something like agriculture and veterinary department in Bulgaria ( in many countries it is possible online) and request for EXPORT permit .
Contact the same in Seychelles and request Import permit .
Last step is finding airline and route that transfer pets and that is more comfy for your fur kid.
Prepare airway bill or get assistance of airline staff on charges and conditions.
Some airline , like Emirates will prepare airway bill and transfer your dog only by cargo.Some will charge as extra luggage or live stock .
One more -IATA approved crate-your dog can stand, turn around and lie down , water container ,good quality material ,hard to brake .
Hope it helped
Good luck
Nadia