I think I have repeated it a thousand times.
Through negotiations. There are tens (if not hundreds) of standardized procedures of negotiation between two belligerent parties. That's why the United Nations were founded.
There are so many lawyers specialized in diplomacy, peace talks. In these procedures.
As far as I know, Putin wants to negotiate.
Does the other party want to negotiate?
Putin has said he wants to negotiate. And he also said a prerequisite for peace negotiations is an
unconditional surrender. Now they are being pushed back, they are demanding peace talks
on the assumption that the currently annexed territories remain under Russia's control.
Putin does not want peace. Period.
Putin wants Ukraine. Period.
So, what do you do when a man like Putin invades a country and refuses to negotiate peace without a total or partial surrender of territory?
What compromise do you believe Putin is willing to accept that doesn't involve Russia annexing at least a huge portion of Ukraine? He is not in a position to make demands of Ukraine or any other country. You do not sue for peace by giving warmongering fascists what they want, and you do not bend over backwards to please people when they invade their neighbours.
Your logic is as if I had broken into your house and refused to leave without you giving your house - or, at the very least, several of its rooms - over to me, and until I get what I want I will keep squatting in your house and punching you in the face. Do you think it reasonable at that point for someone to say "Well, you may not like it, but it's best we don't try to kick them out - because that would be likely require fighting him, and fighting is bad. We should negotiate with him."
No, you would not think that's reasonable.
Because I broke into your house and attacked you. I have no right to your house, I have no right to hit you.
I should not be there. I have no right to negotiate with you over
my share of your house.