This is a complicated and highly specialized area. The question that you have posed cannot be answered in the space available. You need to contact a local atty who specializes in this area of law, if possible dealing with the tribe you are adverse to which is most likely the Sioux. We do not have a Bureau of Indian affairs because this is easy. It not only depends upon the tribe but also mightily upon the kind of case.
You need to bear in mind that there might not be a case regardless of the capacity of the defendant, so be open to that as well and find a lawyer!
In general, Indian tribes have sovereign immunity from lawsuits, unless they have consented to the suit, or Congress has waived the sovereign immunity. Congress has waived the immunity in a few cases, but they are very specific. So, it is not likely that you can sue the tribe. Consult an experienced Indian law attorney in your area.