date - How to convert ISO 8601 formatted DateTime to another time zone in Java?

My current date:
Date utc: 2018-06-06T16:30:00Z (ISO 8601 in UTC)
OR
Date iso: 2018-06-06T11:30:00-05:00 (ISO 8601)
OR
Date epoch: 1528302600000 (Epoch/Unix Timestamp)

I wish to convert the above DateTime to some another time zone areas (like GMT+5:30). And I'm not sure which time format I'll receive from above three. So can I've a generic method which can convert above to some another time zone returning java.util.Date in Java 8?

I did Something like this, But it didn't worked out

public Date convertDateToLocalTZ(Date iso8601, ZoneId toZoneId) {
    Date dateTime = null;
    if (iso8601 != null && toZoneId != null) {
        Instant instant = iso8601.toInstant();
        LocalDateTime localDateTime = instant.atZone(toZoneId).toLocalDateTime();
        dateTime = Date.from(localDateTime.atZone(toZoneId).toInstant());

        return dateTime;
    }
    return dateTime;
}