Pretty much as the tin says, with a POD of the US's founding, somehow find a way to get Native American tribes to have representation in Congress as full voting members of Congress.
Of course, in a few years, the Native American tribes would be a small minority within their own states after white settlers flood in, since by being a state, they cannot bar immigrants from settling in.
Something like the Maori seats in New Zealand? That would be pretty interesting. But it might violate constitutional provisions in various ways, especially if you give American Indians more than their proportional amount of the population. There's about 3 million registered, so that's...one seat. At best, you might be able to get two seats if you include people with noticeable amounts of native blood. That opens up so many issues, the key one being who will represent the native peoples in Congress? You'd need a sort of "pan-American Indian" identity to make it work--that seems much more doable now, but I couldn't imagine it being done when the Indian Wars were in recent memory (at least of tribal elders) and tribes were being pitted against each other. And another big issue--how could you write this into law? Seems like you're inviting some legal challenges and plenty of legal issues.
It would work best at the state level, I think. Some states have very significant numbers of American Indians, and they could end up a powerful voice in the state legislatures. But then you have another issue--do only tribes local to the state get to count/get a vote? After all, the biggest American Indian tribe in many states is the Cherokees, and we're talking about registered members, too. I'm not American Indian, but it does feel a bit wrong to me for a Cherokee living in downtown Los Angeles, say, to have as big of say on the issues of indigenous peoples in California as would, say, a Miwok in rural California, even if the Cherokee in California far outnumber the Miwok and other tribes actually local to the region. It almost feels like it defeats the purpose. And then there's the issue of "local" (Oklahoma might have a fun time with that) tribes if you want to define that, basically it would be a headache with no real solution.
But an interesting thought, though.
I guess I was thinking of some sort of scenario where reservations get federal representation despite being within a state for state government issues. Idk if that sort of quasi status is possible though
Not likely, but you could conceivably have some kind of non-geographic Native American (NA) "state" that encompassed all NAs in the US. It could be given representation like a state, based on population. You could even have 2-4 of these made of of different regional tribal groups. However, it'd be a census, registration, and identification nightmare to determine who gets to vote within the tribal "state" and to ensure those same people don't also vote in "normal" geographic state and municipal elections.
The other way is what you have now -- states get representation. In some states with large enough NA populations, they could control one or more congressional districts.
Finally, you could conceivably have some kind of state secession/realignment option where a portion of a state(s) secedes and applies to be a separate state. For instance, you could have the SE corner of UT, NE corner of AZ, SW corner of CO, and NW corner of NM secede and form a Navajo/Ute/Hopi state. Likewise, big parts of OK could secede and form a NA state. Those may be the only ones that are large and populous to be even remotely tenable.
IMO the easiest way is to expand the Indian Territories to include more than modern day OK and have all the Native Americans moved from their land onto one giant reservation and turn that into a Native American state and give that representation.
The only way that I can think of would be if part of some state seceded from the parent state and joined the union during the ACW. Something similar to what happened in West Virginia. Perhaps the panhandle of Texas? Perhaps western NC? If I am not mistaken the western part of NC was pro-union and a large number of Cherokees had fled there to avoid the Trail of Tears.
In what year would you do this? I recall reading about quite a few conflicts between the Oklahoma Cherokee/allies and the Comanche/allies, for instance. Not to mention all the other tribal groups who just a few decades ago were in open warfare between each other (Plains Indians killed more of each other than the US Army did, for instance). The window between the end of the Indian Wars and the end of Indian Territory is pretty narrow, and in doing so, who's to say you wouldn't re-open some wounds between tribes that would spark violence and demand US government intervention (that would probably not go well).
The government simply wouldn't care much. As far as people of the time were concerned it would be "A bunch of savages are fighting in some godawful piece of desert we don't want anyways so who cares?"