Make your main character to write a letter. Not an email. Not a text message. An actual letter. Who's this letter to? Does the letter explain your main character's relationship to its recipient? Does the reader already know the recipient? Or have you used this opportunity to introduce a new character?
What does the letter say? Do you, as the writer, include the letter in full? In snippets? Or do you simply paraphrase what your character is writing and thinking?
Make sure that this letter offers your readers something new, what is it that we're learning? Everything has to happen for a reason in your story, is this purely to show a character trait? Is it a clue as to what happens later? Is it to put new pressure on the relationship between your characters?
We'd love to hear what you come up with! Feel free to share.