Examiner Path is quite long
First of all, you have to be holder of a flight crew license. Ideally CPL(A) or ATPL(A), but with limited privileges you can also be holder of PPL(A).
Than you have to be a holder of particular rating - for example SEP(land) class rating and extensive experience as instructor on particular class.
Once you have required experience, you have to apply to your state of license issue for examiner acceptance. Once accepted, you have to attend the Examiner standardization. That consists of theoretical knowledge instruction with on-job training resulting into the Examiner assessment of competence done by Senior EASA Examiner.