(a)(1) By resolution of the Indian tribe or Indian tribes to be served; or

(2) When such authority has been delegated by an Indian tribe's governing body to a tribal committee(s), by resolution or other written form used by such committee(s) to memorialize the decisions of that body, if applicable.

(b) In the absence of a designation by the Indian tribe, the default designation as provided in section 4(21) of NAHASDA shall apply.