I think if you just tell us the trip like dub-LHR-jfk-sfo/lax-jfk-LHR-dub format and which segment got cancelled. If the above is kind of accurate and the jfk-sfo get cancelled then you have a few options with that segment if you would like to do it differently however other segments cannot really changed or added extra segments. So you can’t ask to do a LHR-Dub-LHR-jfk-etc -jfk-LHR-dub-LHR as it would need more sector makes no sense for the cancelled Segments point of view. You could play around if timing is required to change for the whole trip but not the order of the segments or the flight.