This article explains how to give a user a nickname within a conversation on Facebook Messenger.
Steps
Step 1. Open Messenger
The icon is represented by a blue dialogue bubble with a white lightning bolt inside and is located on the Home screen (or in the application menu).
If you are not logged in on Messenger yet, enter the e-mail address and password you use to log into Facebook, then click on "Log in"
Step 2. Select a conversation
You can choose a group conversation or a chat with just one user.
Step 3. Click on the "Settings" icon
It is represented by a lowercase "i" in a white circle and is located in the upper right corner of the screen.
Step 4. Choose Nicknames
You will see the names of all the users participating in the conversation.
Step 5. Select the name you want to change
You can change the name of anyone who is participating in the conversation, even your own.
Step 6. Write a nickname
All attendees will be able to see this name, so choose it wisely.
Step 7. Tap Set
The user whose name you changed will appear with their new nickname in the conversation.