JaneBond007
It depends. That's not very helpful.
For the first miracle of JPII, the little sister who had Parkinson disease was reporting to the Mother of her congregation that she could no longer write or exercise her job as a nurse. Then JPII died, then the whole congregation decided to ask JPII to intercede for her. After she was healed, they reported her case (I don't remember if it was to their local bishop or to the postulator of the cause).
The postulator collects evidences and interrogates (under oath) witnesses. A written testimony is also requested.
To be recognised as a miracle, there was the medical council (doctors only), then there was the theologians, then the Congregation for the Causes of Saints and finally the Pope.
The medical council validates if the healing is truly inexplicable. One must have a solid medical record to pass this test.
The theologians validate the spiritual aspect = if the intercession of blessed so and so is involved or is it a case of God showering his grace on someone just because.
Some people, contact directly the postulator of the cause or their priest or their bishop.
For example at Lourdes, people contact the official doctor of the sanctuary.
HTH.