Honestly, you could just create another thread to avoid the controversy that this one created before, or just revive one of the other, relatively less controversial, threads you made.
In any case I think what needs to be done is accelerate the development of large nomadic confederations in the West while hindering those in the East, the 2 things needed would be to have either an Achaemenid-style Persian empire or a more resilient Greek state in the region of south Central Asia able to repel and maintain the frontier against the nomads, thus having the nomads confront with a large state apparatus and having them react by consolidating better.
Also having the Greek, Celt-Dacians stop the Sarmatian expansion into Scythian territory might help that as well.
After you have the conditions to foster such confederation you would need to avoid the Xiongnu from becoming so strong, I guess not having a united China in the medium term would avoid having the same circumstances that lead the Xiongnu to become so dominant, from there I think things would follow slowly their course, obviously it took long for the Turks to properly get into Europe(ignoring the Huns as they relied largely on local peoples to begin with and were not Turk by identity) so I think it might take centuries and a push factors to have some sort of West-to-East expansion of nomadic confederacies.
Although my scenario includes also an eventually Scythian dominated Mongolia, given the trends we saw IOTL being flipped, if you just want a survival of the ancient groups that already existed there it would be even easier, you would just need to avoid the Huns from succeeding or appearing, and this ties easily with pods from the Xiongnu.
It seems like you were implying that Altaics had killed off or drive off those groups.
Well written sources do make the situation seem like that too, I don't think taking a literalist approach is the correct way to go about it, but nomadic territories often had small population densities and more possibilities of population movement, but "Altaics" were mixed themselves and genetics don't match linguistics so intermixing between different groups was present since before settled people started writing about them.
These populations might have even spread into the Xiongnu as archeology says that this confederation was close to 15-20% European.
Xiongnu is said to be a large and diverse confederation containing Huns,Turks,Iranian peoples and possibly Tocharians and Uralic peoples too.
Xiongnu however was limited to the East Central Asia until the Turkic expansions from what I know
That said,I don't think this region can have any shift from OTL unless almost all the Nomadic groups in the East and the West prosper early by giving up Nomadism and get down to Agriculture. It could begin on one of the either side and then be taken to the other group by a small number of migrants or visitors. This could facilitate stable settled empires on both sides. Quite interesting.
To go ahead,we would need a few maps.
You mean West Eurasian?
Actually some recent research suggests that the core Xiongnu elite was Yeniseian speaking and that's were some of the terms like "Chanyu" come from AFAIK.
The Xiongnu fled and eventually became the Huns according to some, this was caused by Han victory against them.
I think the best way to have that would be to corner the nomadic region early on but this can't be done just form internal shift, I think a state like the Seleucids or Achaemenids could achieve something like that in Southern Central Asia, but according to my scenario above this would trigger a escalation of nomadic political organizations, so it wouldn't exactly change the dynamic in the region as a whole.
Same goes for the European steppe, you could have Uralic and Slavic people move in and establish permanent agriculture early on or you could have a change by proxy with a mediterranean state(AFAIK the area of Ukraine did grow grain for Rome too) but you really need to avoid nomadic empires from forming as they would easily sweep away any developing agricultural societies without enough backing.