You generally cannot view messages that were permanently erased from Facebook Messenger
Check archived chats in Messenger
Check the Message Requests folder
Check the Spam folder in Message Requests
Search your email for Facebook notification copies of the message
Download your Facebook information from Settings and privacy
Review any device backups that may contain old Messenger data
Ask the other person in the chat to resend the message
Check other linked devices where the conversation may still be open
Review screenshots or saved copies if you previously saved them