Instead of killing him I would change his destiny to that of a Humanitarian spreading Goodwill instead of harm.
In that way his persona would change by changing his environment to goodwill.
By the way I read his book “Mein Kampf ( my Struggle or My Fight)
It describes the process by which Hitler BECAME antisemitic after he suffered from nerve gas in a war..which probably changes his brain wiring somewhat?
I would go back in time and change that incident so that he does did not become that way.
His mind was still recovering from the chemical shock that changes him when in this state of mind he witnessed a very rich women and richly dressed children walk past a beggar on the street and at this point he chose that women’s Religion as his target for his anger and desperation ( he was starving ).
It doesn’t make it right but it explains where it all started..his hatred etc
Change that incident or even the brain injury itself and who knows what the outcome would had been?
( I think it was tear Gas or something of that nature, not sure).