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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 .
Note that when tener means to have, it does so in the sense of meaning to possess or to own.. The equivalent of the English auxiliary verb to have, as in you have seen, is haber (as in has visto, you have seen).