This refers to Jesus. Translate as "the Word" if possible. If "Word" is feminine in your language, it could be translated as "the one who is called the Word." See how you translated this in [John 1:1](./01.md).
Here "flesh" represents "a person" or "a human being." AT: "became human" or "became a human being" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
The phrase "the one an only" means that he is unique, that no one else is like him. The phrase "who came from the Father" means that he is the Father's child. AT: "the unique Son of the Father" or "the only Son of the Father"
Be careful not to translate this in a way that suggests that Jesus is more important because he is older than John in human years. Jesus is greater and more important than John because he is God the Son, who has always been alive.