Last updated on December 4, 2020
If you already have an account, you can request a mononym by filling out this form. If you’re trying to register for a new account using a mononym, please fill out this form.
Both forms ask you to include both a first and a last name. If you only have one name, you can enter the same name for both New first name and New last name to submit your request.
Once they receive your request, they will work with you to place the mononym on your account.
Source: https://www.facebook.com/help/1090831264320592?helpref=hc_global_nav