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So don't worry so much about how to use  had had  as a unit of grammar, they will come together naturally when you want to express the verb ' to have ' in the past perfect. Let's consider a different verb for a moment like  to want .
Adverbs that tell us how often. Adverbs that tell us how often express the frequency of an action. They are usually placed before the main verb but after auxiliary verbs (such as be, have, may, & must). The only exception is when the main verb is to be, in which case the adverb goes after the main verb.