Instagram is rolling out this feature of allowing one to pin comments.
To access the feature, you will have to update your Instagram to the latest version. Then tap on any of your existing posts and head to the comments section. To pin a comment, simply swipe left and tap on the thumbtack icon.
You can pin up to three comments which will appear immediately under your photo or video with a “pinned” label underneath, next to the “like” and “reply” labels. These three comments will “mask” all other comments which can only be seen by tapping on “view all comments.”
You can pin and unpin a comment as many times as you want. But you should know that each user receives a notification when their comment is pinned (not when their comment is unpinned.)