title: how to roll back changes in a file in a previous commit in git
body: <p>I made 3 'git commit' but I have not done a 'git push'.</p>
  
  <pre><code>1. commit 1
  2. commit 2
     touches fileA
     touches fileB
     touches fileC
  3. commit 3
  </code></pre>
  
  <p>So How can I </p>
  
  <ol>
  <li>roll back changes I made in file b for commit 2? (I can't do a 'git checkout -- fileB' anymore since I already 'git commit', how can i roll back my changes?</li>
  <li>make changes in fileC and make it like part of commit 2? I think I can go and change the file now and then run a 'git rebase -i HEAD~2' Correct?</li>
  </ol>