Duplicate meta descriptions happens a lot more often than you would think. Best case scenario is that Google just ignores the extra meta data but that is still hurting your rankings? How? Well you have wasted a good amount of time working on something that isn't helping your site rank higher. In extreme cases it can even slow down sites (think multiple big & redundant descriptions on a mobile site). Webmaster tools shows duplicate meta description error for blogger homepage and individual item pages that are posts. This doubling occurrence of meta tags for description appeared when blogger introduced search preferences last year that offered blogger users to insert dynamic description for every post they publish. You can find it this option inside blogger post editor named with Search Description and you can add any description to the specific post.
How to fix it on blogger
1. Go To Blogger Dashboard > Template
2. Please Backup your template in your computer drive.
3. Click Edit HTML and Search for the following code
<b:if cond='data:blog.metaDescription != ""'>
<meta expr:content='data:blog.metaDescription' name='description'/>
</b:if>
4. Replace above with the below code. If you can’t found above code, then you may simply copy the below code and paste it just after opening <head> tag.
<b:if cond='data:blog.url != data:blog.homepageUrl'>
<b:if cond='data:blog.pageType != "item"'>
<b:if cond='data:blog.metaDescription != ""'>
<meta expr:content='data:blog.metaDescription' name='description'/>
</b:if>
</b:if>
</b:if>
5. Save your template and you are done! Now visit your homepage or any post page to check its source file.
I hope this improvement will help robots to better crawl and index your content. Please let me know below in the comment form if you needed any help.