Dear Ms. Moyer,
Thank you for posting your request on History Hub!
For an overview on how to begin your research, we suggest that you review NARA’s Native American Heritage as well as the FamilySearch Research wiki for Indigenous Peoples of the United States Genealogy. We also suggest that you search the various Free US Indian Census Rolls 1885-1940 that are organized by Tribal Nation for mention of your relative. Please review NARA’s web page on Indian Census Rolls for more information
When embarking on Native American genealogy, please note that the records in the custody of NARA often only detail those living on the reservations or being administered by the Bureau of Indian Affairs. If an ancestor was Native American and left the reservation or did not have interaction with the United States Government as such, they will not be recorded in NARA’s records and tracing their genealogy may be difficult.
You may also wish to reach out to the Citizen Potawatomi Nation which is located in Oklahoma to research how to determine if William Dancer is recorded as a member of their tribe.
I could find no record of the Lakota in Oklahoma or Tennessee and most of the federally recognized reservations for the Lakota are in North and South Dakota, Minnesota, and Nebraska.
We hope this is helpful. Best of luck with your family research!