The proof never comes from the Bible, does it?
Look at the "proof" provided by the JWs to their converts. These "converts" are, by and large, already Christians and thus already believe the Bible. So the "proof" is simply in the skillful manipulations of Biblical interpretations, twisted logic combined with aggressive mind control techniques.
Now let's move to Awakened's scenario with the tribe who has never heard of the Bible, and in fact, has their own established belief system.
The proof must come in the form of something other than an appeal to logic.
There is a South Park episode in which Christian missionaries are trying to teach the Gospel to starving Ethiopians, who are so hungry they occasionally try to take bites of their Bibles, provided free of charge by the missionaries. In Bible class, the Ethiopians are uninterested in study until the missionary promises food as the reward for Christianity.
Let's see... how were the Native Americans converted? Hmm... does the term "conquistador" come into play here?