It depends on what you are trying to say.
If you mean "congregation" as a "large grouping", such as "A
congregation swept by the store with none entering", then the
translation would be: "Soy de una congregación de ingleses."
If you mean "English congregation" as "from an Anglican Church",
then the translation would be, "Soy de una congregación
anglicana."
If you mean "English congregation" as in "a religious
congregation made up of Englishmen" as opposed to necessarily
Anglican, such as "I am Muslim, but from an English congregation as
opposed to a Pakistani one", "Soy miembro de una misa inglesa."