To borrow from a previous answer I wrote on this topic:

The association of the Swastika with far-right, anti-Semitic, and völkisch (A populist racial-nationalist movement) groups in Germany predates the Nazi party. One of the early, prominent examples was Adolf Lanz, a turn of the century racist who published a magazine called Ostra and also had an obsession with the Templars, founding the "New Templar Order". He used the symbol, along with with other signs that were considered "mystical". Lanz himself was probably influenced in its use by Guido List, an early writer on the supposed supremacy of the Aryan Race. According to him, the Swastika was the symbol of the "Unconquerable Germanic Hero" and "The Strong One from Above".

These early users were certainly aware of its Hindu usage, but to them the symbol was an Aryan one (one which, in the pseudo-racial theories they subscribed to Aryans brought to India presumably). There may have been earlier users within the movement, but certainly by the early 1900s, it had come to have strong association with far-right, racial politics in Germany.

Contemporary to the Nazi Party, the Deutschvölkischer Schutz und Trutzbund, founded in 1919 as a way to collect together many of the small völkisch under one umbrella, adopted the swastika as its symbol, as the did Thule Society, a völkisch/occultist group that was influential on the early Nazi party, and some of the Freikorps during that period used it too.

So when the Hitler chose the swastika as the party symbol in mid-1920, he hardly did so at random. It had already become strongly associated with the völkisch movement in Germany, and as the party was still small and trying to grow in membership, it was a clear way to tell people at least in the broad strokes what the party was about.

Hitler: 1889-1936 by Kershaw; The Coming of the Third Reich by Evans