Can/How do you delete a location attached to an already sent facebook message?

Nope. What’s done is done.

Maybe. Some Facebook posts are dynamic, which means that they pull data afresh each time someone accesses them. This means that blocking the app that tells your location might remove that data from old posts. It’s a long shot, though, and you’d have to be okay not using the app anymore. Why not just try deleting the message itself and resending it?

@Patton Because from my understanding, even if I delete the message from my inbox, the recipient still has it in their message. Is this true?

Would it work if I report the message and block the person?

@Wine No, I don’t think that’s true. I think the message is shared data. You and the recipient see the same thing, so deleting it makes it unavailable to both of you. Reporting and blocking should also work, though.