LinkedIn Android App unarchiving
You can archive a message instead of deleting on LinkedIn's mobile app but you can also easily unarchive the same conversation.
Archiving a conversation:
Open the LinkedIn app > then tap on the Messaging tab.
Find the conversation that you want to archive and press and hold it.
You would get a pop-up and you would have to tap on Archive conversation.
Open the LinkedIn app and in the Messaging tab find Filter on the top right and tap on it.
Tap on Archived in the menu.
You can view a message by tapping on it.
Now, you can unarchive the message, by tapping on the thumbnail found on the top right of the conversation.
Now, in the Conversation actions, tap on Restore.