If you've got an FAA ATP and 500 hours multi crew then required steps are:
1) get an EASA class 1 medical (about $900)
2) register with the CAA online portal and self certify for the exams (free)
3) Study all the question banks you can find (virtually free)
4) take the exams (about $100 each)
5) find a SIM and examiner to take an LST in whatever type you have on your FAA cert.