You can literally read up on ancient people's myths, deities, etc. that are build around eclipses, or even just the sun itself.
That being said. A lot of uncontacted tribes are not completely oblivious to the outside world because they are by proxy in contact through other tribes that are contacted, exchanging knowledge.
Good point. Total eclipses, however, are very rare, occurring at a given location on the Earth only once every 400 years (or so). Given how small a range any modern uncontacted tribe would be, it's unlikely that anyone but their remote ancestors experienced a total eclipse. And there's a massive, inexplicable difference between a 99% eclipse and a total eclipse. A 99% eclipse briefly makes things darker, a total eclipse changes reality; the visual effects of what you see are disorienting, at best.
So: yes, uncontacted tribes may have seen the sun get briefly dimmer. But even in more "modern" cultures, total eclipses have been cause for hysteria and panic. And maybe that's the best answer to OP's question: take a look at recorded history, e.g. Ephraim Miller and the total eclipse that passed over Texas in 1878.
They probably do get nervous. One of my favorite eclipse stories to read about is in Guna tradition in indigenous central America, where albinos, who are all said to descend from a single Zoroaster-like sage, are said to be imbued with magic powers from birth because they're seen as being born of the moon. And when a solar eclipse happens, it's up to them to decide if the Earth is worth saving from the dragon that's eating the sun. The tradition lives on enough that almost half the population is albino as their popularity there was self-boosted in ancient times.
I wonder if this is the inspiration of the moon arc from Avatar.
I have no academic basis for this but I kind of imagine any remaining uncontacted tribes are sort of mangled versions of the cultures they descended from. They've been kept small and isolated so their oral traditions may have become severely warped and may essentially be tiny 'cult-of-personalities' of a few people's ideas that have very little similarity to more ancient traditions.