1. Log in to your blogger account
2. Go to Design --> Edit HTML
3. Check in the "Expand Widget Templates" box
4. Find this code
<dd class='comment-footer'>
But, if you didn't find that code, try to find this code<b:include data='comment' name='commentDeleteIcon'/>
5. Then, copy the code below, and paste under one of the code above.<a expr:href='"https://www.blogger.com/comment.g?blogID=Your Blog ID&postID=" + data:post.id + "&isPopup=true&postBody=
%40%3C%61%20%68%72%65%66%3D%22%23" + data:comment.anchorName + "%22%3E" + data:comment.author + "%3C%2F%61%3E#form"' onclick='javascript:window.open(this.href, "bloggerPopup", "toolbar=0,location=0,statusbar=1,menubar=0,scrollbars=yes,width=450,
height=450"); return false;'><img alt='Reply To This Comment' src='https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidnSKhaPM4yqlsd47qzdvSyYWHonml3-eOa73peMIxYudv5LWQyFMmLnqRqfjEAmN_My86seMJdBT8SCcMVLWVIuUUvu92QG-69Oq4FI91n2Dgzm7B8CCVcQBR9NzQqiLNstlf4HSYy2A/s1600/reply.gif'/></a>
Customize:%40%3C%61%20%68%72%65%66%3D%22%23" + data:comment.anchorName + "%22%3E" + data:comment.author + "%3C%2F%61%3E#form"' onclick='javascript:window.open(this.href, "bloggerPopup", "toolbar=0,location=0,statusbar=1,menubar=0,scrollbars=yes,width=450,
height=450"); return false;'><img alt='Reply To This Comment' src='https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidnSKhaPM4yqlsd47qzdvSyYWHonml3-eOa73peMIxYudv5LWQyFMmLnqRqfjEAmN_My86seMJdBT8SCcMVLWVIuUUvu92QG-69Oq4FI91n2Dgzm7B8CCVcQBR9NzQqiLNstlf4HSYy2A/s1600/reply.gif'/></a>
Your Blog ID can replace with your blog ID, the location of your ID is in the address bar
http://4.bp.blogspot.com/_mWrR0gomZ0/TIIfWolwWgI/AAAAAAAAARE/nwiHJLeqSVw/
s1600/reply.gif is the "Reply" button, you can change with your own.
6. Finish! Just click Save Template
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