That is a trick question. One would think the obvious answer is a long recitation of retorts such as stop creating chaos and deliberative combativeness inside and outside of the White House, eliminate the hate-filled rhetoric both in person and in his tweets, stop lying to the American people, stop coddling some of our worst enemies abroad, and the list goes on and on.
Listen to or read the works of psychologists across America who by now have weighed in on Trump's behavioral problems and you will see common agreement on the severity of the issue. In a revised and republished study by Brandy Lee, M.D., M. Div., titled The Dangerous Case of Donald Trump - 27 Psychiatrists and Mental Health Experts Access a President, Lance Dodes, a former assistant professor of psychology at Harvard School of Medicine, writes, "Mr. Trump's sociopathic characteristics are undeniable. They create a profound danger for America's democracy and safety. Over time these characteristics will only become worse."
So as to the correct answer for what can Trump do differently to bring the country together? The answer is nothing. His mental state is growing worse with time, and you don't really need to be a shrink to see it or understand it. Trump is too far gone and incapable of making such drastic changes at this stage in his life. What you see is what you get and we are stuck with it, at least for 382 more days.