https://www.govinfo.gov/app/details/STATUTE-71/STATUTE-71-Pg...
is an example. Currently however congress has tried to improve / make up for prior poor treatment of native americans - but the power is ultimately in congresses hands (with some small limits).
Trump was active in this more recently
https://www.theguardian.com/us-news/2020/mar/31/trump-admini...
The decision was that congress had not disestablished the reservation as part of the Oklahoma Enabling Act of 1906, and so they could not be convicted in Oklahoma courts.
This emphasizes, not diminishes, congresses role in deciding what reservations are established or not.
They could do something about it, but they need to pass a law to do it. They can't just do it without changing the law.