step 1: log into facebook if you aren’t already.
Step 2: go to: facebook.com/username
(You will see a page like the one below)
Step 3: Click "set a username" for your Pages.
Step 4: choose which page you want to set the username for:
If it is not eligible to choose a username, then you will see the message above.
How do you solve that problem? Get some more fans.
Step 5: If you see a box pop up that asks you to enter a username, do that, and the click "Check availability"