You will probably be able to extend your flight through the airline company. Keep in mind that if you are not planning to return with your group on the same flight you must make your changes before the conclusion of the trip and before the group return date. You will be responsible for your own PCR test prior to returning to the US. Note that traveling to other countries after the trip is not permitted this season because the permit they have for entering Israel is only for one entry to Israel. Participants with Israeli passport do not need a permit, so they can travel.