How to Add WhatsApp Share button in Blogger Blogspot
Log on to your Blogger Dashboard
1) Click on Template->Edit HTML
Go to mobile-post and expand as shown below.
2) Copy and Paste the following Code under (clear for photos floats)as shown in the below image.
Save the Template.
3) Now go to Templates -> Mobile -> Choose mobile template -> select Custom and save the changes. Now you can browse your website through Mobile and check.