I understand that one of the first instances where indigenous peoples used firearms (at least in South America) was in 1558 during the battle of Quiapobattle of Quiapo, where a Mapuche army of 6,000 warriors had approximately 20 arquebuses and 2 cannons (All the equipment previously captured in Marihueñu) and defended a fort against Spanish forces.
It is clear to say that they aim was not good. Although a few would stand out, such as the Toki (Warchief) Ñamku better known as "Mestizo Alejo".