Changing og:description on WP site

I'm wondering if you're able to help me - a couple of people have asked me how they can change what facebook automatically displays as the exerpt when linking their website.
I've checked on the developer sharing debugger on Facebook ( but other than seeing that it's the og:description meta tag that needs changing, I'm not sure how to proceed. I'm guessing I just need to change the information on one of the pages, but I'm not sure which and I don't really want to go poking around without being sure. Alternatively, is there a plugin that can assist?
I'd really appreciate any guidance on this!
Thank you, Stacey