Having the Battle of Trafalgar won by the French would be a start, though I wonder if Napoleon could also be able to capture London as well. Other than that, not sure if Napoleon would want to have a long, protracted war in the British Isles.
Victory at Trafalgar wasn't decided by the toss of a coin, there were numerous
reasons why it was a British victory and you'd need a POD significantly earlier -- probably even before the French Revolution -- to give the Franco-Spanish combined fleet a significant chance of success there.
And even if the Franco-Spanish fleet had won at Trafalgar, Napoleon had already given up on waiting for its arrival in the Channel by then and had marched his army off inland to fight a campaign in eastern Europe instead.
And by the time that he could have tried again we could have assembled another strong fleet, under another good admiral, to hinder his plans.