You need to contact the airline’s office in Israel directly and ask for their assistance. They may ask for your confirmation number, or PNR (you can find the code in the confirmation email you have received regarding your extended flight or from your group leader).
Please check here for your specific airline phone number or contact.
Please note: Other branch offices and call centers of the airline cannot assist with Birthright Israel tickets. In other words, do NOT call the general “800” number or other customer service numbers for your airline.