First, an expedition would set out from a nearby, newer colony.
Secondly, after they arrive, they speak to the locals to figure out who is the strongest group.
Thirdly, the Spanish would meet with the leader of the powerful group, and exchange gifts. They would kidnap the leader after this, threatening to kill them unless their followers obeyed them.
If they did have to fight, the Spanish would try to fight on an open field and their technological advancements would give them a huge advantage.
Lastly, the leader of the expedition would stay back and become the leader of the new colony. They would take the natives into slavery. His second-in-command would lead a new expedition, in order to find a new colony.