title: Replace character in a string using awk or sed
body: <p>Given the string below, how can I replace 6th and 7th by getting 14th and 15th digit using awk or sed.</p>
  
  <pre><code>xxxxx02xxxxxx89xx
  xxxxx22xxxxxx33xx
  </code></pre>
  
  <p>output</p>
  
  <pre><code>xxxxx89xxxxxx89xx
  xxxxx33xxxxxx33xx
  </code></pre>
  
  <p>I am newbie here, sorry for my question.</p>