How can Russia (eventually) return to the Council of Europe?

[LAKISYLVANIA]

None of this will occur, Russia is not a European nation, and the very principles upholding the COE are under strain right now

Was Germany an European nation between 1933 and 1945?

Genocide and aggressive war is keeping well with European traditions so Germany fits in well there, meanwhile Russia has never been properly accepted as European by Europe itself and does not have the institutions nor post war patron to rebuild a la Germany

Your definitions of Europe are preposterous, to put it mildly. Either Europe has some definition that is unambiguous or it's nothing more than a vainglorious title of a self-defined club of countries. Russia is historically, culturally, linguistically and even geographically (for most of the population lives in the European part) part of Europe, no matter how much the rest of the continent hates them.

Do you believe Turkey is European? Would your answer be different prior to ww1 when there were millions of Greeks still in Anatolia

If Ukraine and Belarus are Europe, so is Russia.

Most of Russia's population live west of the Urals, it's in every way culturally and geographically Europe.