How to convert DateTime<UTC> to DateTime<FixedOffset> or vice versa?

I have a struct that contains a timestamp. For that I am using the chrono library. There are two ways to get the timestamp:

1. Parsed from a string via DateTime::parse_from_str which results in a DateTime<FixedOffset>
2. The current time, received by UTC::now which results in a DateTime<UTC>.

Is there a way to convert DateTime<UTC> to DateTime<FixedOffset>?

I believe that you are looking for DateTime::with_timezone:

use chrono::{DateTime, Local, TimeZone, Utc}; // 0.4.9

fn main() {
    let now = Utc::now();
    let then = Local
        .datetime_from_str("Thu Jul  2 23:26:06 EDT 2015", "%a %h %d %H:%M:%S EDT %Y")
        .unwrap();

    println!("{}", now);
    println!("{}", then);

    let then_utc: DateTime<Utc> = then.with_timezone(&Utc);

    println!("{}", then_utc);
}

I've added a redundant type annotation on then_utc to show it is in UTC. This code prints

2019-10-02 15:18:52.247884539 UTC
2015-07-02 23:26:06 +00:00
2015-07-02 23:26:06 UTC