Upvote:1
For a purchase made on a single ticket, call the airline to reschedule as soon as possible. Otherwise, it will be up to you to reschedule the second flight yourself and incur an applicable penalty since both flights would not be related from a booking perspective.
Normally, when an airline reschedules a flight, they automatically reschedule connecting flights but I've seen it happen quite a few times that it either fails to reschedule or the new schedule is impossible, such as arriving at your destination after your return flight. It's impossible to say why that happens sometimes but is most likely a bug in a system when there are massing routing changes or cancellations at the airline or one of its partners.
You should proceed to contact them quickly because your options tend to get less desirable as people rebook their trips. It is likely your first flight will be rescheduled again if they cannot find a suitable connection which is often the case then the entire trip did not get rescheduled simultaneously.
Upvote:4
If both flights are on one ticket you don't need to worry, the airline has to reschedule the connection flight too. If you booked 2 separate tickets it's up to you to reschedule or book a new connection flight.