In a recent update, Instagram added the ability to edit posts and pin and unpin chats. This feature is available in many messengers; you can usually pin 3 to 5 chats to access them quickly and not have to search for them in your inbox.
Now the same feature is available on Instagram and you can pin up to 3 chats.
To do this in your Inbox, swipe left from the right edge and tap the “Pin” button.
If you want to unpin a chat, you need to do the same and tap on the “Unpin” button.
I think everyone knows what pinned messages are. But for those new to this, these chats are independent of when the last message was sent. So they don’t go down over time when no one sends messages there.