If you received a single message stating that the departure time has changed, but the ticket does not need to be reissued, you can arrive at the airport according to the new departure time and do nothing further. Your ticket is valid and does not require reissuance if the departure date and flight number have not changed.

Other options:

Flight number and/or departure date changed

Departure time changed by more than an hour and it doesn't suit me

I received two messages: one states that the ticket does not need to be reissued, and the other states that it does. I can't figure it out