You get the bombs to stop falling.
Assume, like Finland had to that Ukraine concedes the occupied lands as they stand today, that leaves all four regions he declared annexed as not totally part of Russia, so he's going to want land his army has not already taken. He'll want the part of Russia taken by Ukraine back too, he won't be able to sell anything less to his people.
Back to Finland, they gave up the ruined bits that Russian had destroyed, the populations of those areas, 99.9% of them went to Finland, that land still today, nearly 100 years later is still a ruined wasteland, that's what will be what Putin takes from this, a bunch of ruined towns and cities. He will also not be able to sell to his people Ukraine joining the EU and/or NATO, those ideas must be off the cards.
There will need to be policing of the new border, who is going to do that and what will they do once Russia has re-armed and comes at them again? Back to square one with the fear of escalation.
So you are negotiating for Ukraine's position, what would you suggest?
And then there's the matter of the stolen children to deal with, alongside Putin's arrest warrant that he absolutely wants rescinded.
I'm genuinely interested to know how any of the above can be realistically be achieved without Ukraine being another Belarus.