Japt -P, 9 bytes

¸Ën"FB" d

Try it

¸Ën"FB" d     :Implicit input of string
¸             :Split on spaces
 Ë            :Map
  n"FB"       :  Convert from base "FB" to decimal, ignoring all other characters
        d     :  Get the character at that codepoint
              :Implicitly join and output

Japt -P, 9 bytes

Or 8 bytes if input can be lowercase.

¸Ën"FB" d

Try it

¸Ën"FB" d     :Implicit input of string
¸             :Split on spaces
 Ë            :Map
  n"FB"       :  Convert from base "FB" to decimal, ignoring all other characters
        d     :  Get the character at that codepoint
              :Implicitly join and output