Read txt file line by line, check if input string matches content of txt file, C#

I am trying to create a login method that checks a text file called accounts.txt that has a string such as "Bob password" already logged in it. The parameters, "login" being command, "Bob" being param1 and "password" being param2

When I run command line arguments, an example would be "login Bob password" the check should read contents of the file line by line until it finds a match and returns "login Bob successful" otherwise say "invaild username/password"

Not sure how to go about this, any tips are appreciated

protected void login(string command, string param1, string param2) // string command "login" string username, string password
{
    // login command
    // Needs to check accounts.txt file for username and password.
    // if username and password exists, provide logon message
    // if username and/ or password does not exist, provide failed logon message.
    // IN MEMORY store current login username and password

    //checks accounts.txt file if username already exists and if there is a match

    if (not sure what arg would go here)
    {

        string path = "C:\\Files\\accounts.txt";
        Console.WriteLine("username and password match", path);
    }
    else
    {
        Console.WriteLine("Login Failed: invaild username or password");
        string path2 = "C:\\Files\\audit.txt";
        using (StreamWriter sw2 = File.AppendText(path2))
        {
        sw2.WriteLine("Login Failed: Invaild username or password");
        }
        throw new FileNotFoundException();
    }
}