Originally Posted by CarefreeBA

Dropping the leg would work, if the departure point was within 300 miles of LHR. However, the best thing to do here would be to change the departing point up to 300 miles and move it -3/+14 days. So an example would be day 1: IST-LHR, then day 3: LHR-JFK. I’m not sure if you are already booked on optimal flights, but take this opportunity to adjust your LHR-JFK and JFK-SFO legs should you wish to ideal timings as you have the freedom to. Once you confirm the flights, you can no longer make those changes (subject to your ticket rules).