1. Now go to Blogger Dashboard > Template
2. Download a copy of your template
3. Click on Edit HTML
4. Hit Proceed button
5. Check Expand Widget Templates checkbox
6. Find below code in your template
<div class='descriptionwrapper'>
<p class='description'><span><data:description/></span></p>
Now Add your search box code immediately after these lines.
7. Save the template.That's it :)