In the first place, you need to select the FB Page that the ad belongs to.
Then, you need to click on Choose Existing Post and select "Find By Post ID" option. It will open up the box and you can copy the extension of this post's link.
Unfortunately, it is not possible for clients to find a campaign by its Facebook Post ID.
Our tech team can reach this information from the backend.
Important note: One post may have been used in any campaign temporarily. It's not possible to check that.