I'm afraid I can't provide specifics as to the names given to the Amazon River prior to Western settlement, but it's important to point out that the Amazon river is 4000 miles long and basically bifurcates a continent. Many native tribes lived and continue to live near it all of who did not have contact with the rest. Those in close vicinity to other tribes may have had some trade or cultural exchange, but there will be no one answer to the question "What was the Amazon called before it was the Amazon?" because every language will have its own name for it.

I can't answer this question but I'd like to state that Orellana didn't "change" it's name. All he did (and was it even him, or Charles V?) was give it a name that Spaniards, and later other cultures who learned of the river from them, would call it.

It's really difficult to "change" the name of places across multiple cultures.

Let's take Germany.

Many cultures call Germany "Alemannia," especially those in the Middle East and even countries in their neighborhood like France, Spain, and Portugal

Heck, Germany is basically what Anglophones call it. The Germans themselves call it "Deutschland" and call themselves "Deutsche."

Most likely the natives have a name for the river that resembles the name they had for it 500 years ago, if they ever named it.

I hope someone answers your question because I'm working on a project involving Orellana and the Amazon River.