Appears to be a way to ask, "How do you say...?" or "What do you call...?" (i.e. in Kumeyaay).
'ich: a shortened form of 'uuch "what?" usually used when asking what someone is named.
miich: "you say", second-person singular of wii (wip) "says", with the -ch suffix, which is either for emphasis, or may originally be the -ch same-subject suffix, though a second verb is not found in this phrase.