You have all the powers that Putin currently does. Everyone completely loyal to Putin is now loyal to you. Enemies of Putin are enemies of you. Putin no longer exists, and there has been a clean and absolute transfer of power to you. The economic, military, social and political situations are the same as they now are. You are not inhabiting Putin’s body, you are just you. You’re magically transferred to the Kremlin. The world at large doesn’t know your past life, to them you have magically appeared as the new ruler. To everyone who knew you before, you just vanished.
Edit: no one knows your past life YET. They’ll quickly figure it out. You will not lose any support based on your actions in your past life.
End the war, arrest and imprison all oligarchs, declare the rebirth of the RSFSR (Russian Soviet Federative Socialist Republic)
What do you do about the generation of Russians who have lived West of that border their entire lives?
This is the real rub about border disputes that last more than a few years.