There are two ways to unblock someone on Messenger, depending on whether you’re using the Facebook website or the Messenger app:

Unblocking on Facebook Website:

1. Go to https://www.messenger.com/ and log in to your account.
2. Click the Messenger icon in the top right corner of the screen.
3. In the Messenger menu, click on the three dots menu for settings.
4. Select Block settings.
5. Click on Edit next to Block users.
6. Choose See all blocked users.
7. Find the person you want to unblock and click Unblock next to their name.
8. Confirm by clicking Unblock again.

Unblocking on Messenger App:

1. Open the Messenger app on your phone or tablet.
2. Tap your profile picture in the top left corner.
3. Scroll down and tap on Privacy.
4. Select Blocked Accounts.
5. Find the person you want to unblock and tap on their name.
6. Tap Unblock to confirm.

By following these steps, you’ll successfully remove the block on the chosen person, allowing them to send you messages and see your online status on Messenger again.