Find your form. To search, type in a keyword and/or choose a category. To search for archived forms from a previous tax year, choose a year in the drop down menu.
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 .
The tense can be shown in the verb. For example, am, is, and are are always present tense, and was and were are always past tense. Or the tense can be shown by adding words to the verb. In English, the words that we add to the verb are helping verbs or auxiliaries, like be, have, shall, will, and so on.