Hi MNZ,
Congrats for receiving your SA and upfront medical.
As networkjas mentioned, you just have to call the panel physician for an appointment or in other countries just like ours (Philippines), no need for an appointment but we have to be there early coz they can accommodate for just so much people. They may ask your parents to bring pictures and copy of passport so it's best to call them first and ask what the applicants need to bring with them. After the medical tests, they will be given a document that medical was completed. The results will be forwarded directly by the panel physician to CIC.
With regards to paying the rprf, networkjas also gave the link. After paying it online, you have to send a copy to New Delhi where your parents' application are being processed. Also, send a copy of any document that your parents received after completing the medical just to make sure CIC knows that you already complied with their requirements.