Having read An American Genocide by Benjamin Madley, how might acknowledging the reality of United States history help to transform your understanding of your identity, your community or group, your view of others, and your sense of the importance of history?

Your question can be answered from more than one perspective. For instance, for those whose ancestors were already in America between 1846 and 1873, especially in California during those dates, there is a great potential for a transformation of understanding identity, community, group, others and history. While for those whose ancestors came to America after those dates the potential for transformed sense of self and community is, it seems, both less and different, although the potential for a transformed sense of others and of history seems equally great.
As one instance to consider for an example, both my maternal and paternal ancestors came to America in 1907 (pure coincidence), and while, as a first-generation American, I don't feel a shift in my identity, I do feel a new sense of shame, regret and sorrow over the events Madley reveals as having been foundational to the existence of my home state of California. My sense of community, though not transformed, is jolted since some of the questions I've had since high school about Central California Indians have found such unsettling answers.
Madley might suggest the important transformation is toward a view and toward actions that accord with the 1948 U.N. Genocide Convention that defines genocide and details genocidal crimes. He might suggest that our transformations in our perceptions of self, community, others and history should help us to answer the questions raised by his discussion of "intent to destroy a group" in California and to demonstrate our commitment to deciding honestly on the issues of apology and reparation.

   Genocide, however, is more than an academic concept. It is a crime defined by an international legal treaty and subsequent case law. On December 9, 1948, the UN General Assembly adopted the UN Genocide Convention and its genocide definition "unanimously and without abstentions." ... [It has been] signed or acceded to by 147 nations and is supported and further defined as a legal instrument ....
https://history.ucla.edu/faculty/benjamin-madley