If you are strictly using the Messenger app and want to unblock someone you have "Ignored" (moved to Spam) rather than fully blocked:
This is the most common method for Android and iPhone users. how to unblock people on facebook messenger
: Tap the gear icon (Settings) located in the top-right of the menu pane. If you are strictly using the Messenger app
This is the most common way to manage your blocked list. they can message you again
Once unblocked, they can message you again, but your past chat history may or may not reappear. If it doesn’t, you can start a fresh conversation.