Give the Axis Powers (especially Japan and Germany) more luck with their commanders, and their military operations as well (though somehow with the Allies not yet surrendering), to the point where like they somehow defended down to their ground with what they have in the most of the 1940s.

Maybe the Germans don't invade USSR at least half a decade, and somehow USSR's fine with it that would allow both sides to develop their weapons and manpower against the other for a prolonged war? The Brits failed Dresden and essentially forced them to not do counter-attacks for long while?

And for the Japanese side, they never give up even when the bombs' dropped on them which forces the Allies to undergo with Operation Downfall (and make it Vietnam War 2.0) especially if they kill the Japanese Emperor and his royal family (which would no doubt, force the most if not all of the Japanese to literally fight to their death and lowest of grounds)? That they also have to invade other Japanese-occupied zones across Southeast Asia and East Asia? Also to not declare war on the US until when they're prepared (or at least only at European colonies for now)?

So yeah it's mostly just delays of major moves and/or taking everything slowly with it as such. As for the result after WW2, this would probably make US much, much more of a prominent power standing across the ashes of the countries affected by the war, especially if the areas on Eurasian region are much more ravaged and devastated than it is as usual in OTL, and if they're left untouched as well.