How do I change the icon that posts with my blog posts to social media?

Do you use any sort of plugin for posting to social media? Proper plugins should be delivering appropriage OG data to get the right picture, etc.

What exactly are you doing to see this?

Are you copying a link on your site and pasting it on Facebook?

Need more details and a link would be helpful.

WordPress does not do that automatically

So you either have a plugin, or possibly a theme feature, handling this for you.

To be able to further troubleshoot, we would need to know what if handling the functionality for you

Ah, then you would need to check with them.

Since that appears to be a service, we cannot investigate what is happening behind the scenes there. No way for us to help!

Check with them, see if it’s something on their end, or something wrong with your site. If it’s a site issue, then maybe we can help.