How to overwrite the .replace line?

Question

Java

Hello everyone, I don’t understand what is the reason)
The essence of the task is to find a line in the file with the same value as the variable and note this line.
The line is located but not overwritten in the file, maybe someone knows how to fix it)

Here is the code:

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class main {
    public static void main(String[] args) {
        String str = "qwerty";

        try (BufferedReader br = new BufferedReader(new FileReader("C:\\Users\\***"))) {
            String line = br.readLine();

            while (line != null) {
                if (line.equals(str)) {
                    line = line.replace("qwerty", "str1");
                    System.out.println("Replaced " + line);

                }
                line = br.readLine();
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Answer 1

I see reading from a file. Where is the entry to another file?
Why is the file not closed?