Check Archived Chats in Messenger
Open Messenger and use the search bar to find the conversation
Review Message Requests and Spam folders
Check if the conversation exists on another device where you are still logged in
Download your Facebook information from Settings and Privacy
Select Messages when requesting your data download
Wait for the download link and review the exported files
Ask the other person in the chat to resend the messages or screenshots
Check connected email notifications for message previews
Restore from a device backup if Messenger data was included
Contact Facebook Support if the messages were tied to an account issue