This can be done by creating a blog post template. We have a guide here that covers how to create a blog post template in your theme. From there, it also shows you how to assign that template to a blog post. I have created a screen recording here that will show you how to create the blog post template in your theme files to include a link at the bottom of your posts, before the comments section.
Once you create the blog post template, you will want to assign the template to your blog post. Our guide here covers that.
If there is anything else I can help you with, please let me know.