The Soviet leadership at the time you go back to will absolutely follow through on your advice.

For me, I'd go back to say the early 60s and tell them to invest absolutely everything they can into computers, cybernetics, linear programming, etc; and using those tools for optimal central planning of the economy. Optimal both in the sense of economic efficiency and for greater democracy in the planning decisions. Get people to feel like they have a say in the economic plans and I think you short-circuit a lot of the consumerist drives. But ultimately, you just need that computing power to run a modern centrally planned economy.

I thought about telling them to make a Xi-like anti-corruption push in the 70s or so (and Andropov was working on that before he died). But I think if you get them to focus on the stuff I mentioned above a lot of the corruption might ultimately sort itself out.

I also thought about telling Stalin that he really needs to think about maybe approaching collectivization of the farms a bit differently. But I don't know what I'd tell him to do differently though. It was a mess at first but eventually the collective farms helped get Soviet agriculture where it needed to be, I think.