It is a little more complicated when there is a code share flight, like Air France for VA and DL. So, if say VA has a sked change it goes through the AF system, advising the TA through their system, then they advise you.
Just a round a bout way. If you go onto the VA website and DL website, make sure your information is up to date, phone number, email, frequent travelers numbers, etc. So, if they have a sked change you will be advised.
You should check the schedules periodically, no matter who booked it, to make sure it’s still good. Sometimes, its very minor or just a flight number change. I download the airline App on my phone and check it often. Useful for checkin also.