Steps to apply fontawesome on any button, label etc
-
Select the Font Awesome 5 (Brands)[in your case] from Font Typeface drop-down
-
Enable the HTML Format option from Advance properties in designer section
- From Font Awesome website copy the code as shown below
- Paste that code in the text field in following format

After everything done it will look something like this 
(See the red underlined fields)
Result:
