You have to use the formatter when parsing the date string. Also you need to tell it to change the zone or zone offset to get it into AEST/AEDT.
This might work:
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSXX");
ZonedDateTime zdt = OffsetDateTime.parse(input, dtf)
.atZoneSameInstant(ZoneId.of("Australia/Sydney"));
String dateInTimeZone = zdt.format(dtf);
The offset will appear as “+1000” or “+1100” depending on the time of year.