I think that many Trump supporters simply cannot be wooed by the Democrats by any legitimate means because of their racism or other extreme right-wing views. But I do think that a goodly percentage of Trump voters would be open to a populist approach if it was presented in a way that they would not have to admit that they were wrong to support Trump. Perhaps an argument such as,
"We understand your anger and frustration as you were being left behind in the economy. We understand your fears as what were solid jobs disappeared and your own financial situation became more and more marginal. We understand why you wanted to change the business-as-usual thinking in government that appeared to ignore you and your problems. We understand how Trump spoke to you on these issues and why you hoped he would be the one, the outsider who would help you. But sadly he lied, he betrayed you! You counted on him caring about you, but he turned out to be just another lying billionaire seeking to line his own pockets and the pockets of his wealthy friends. Rather than trying to solve your concerns he only cynically exploited them for his own benefit. You only have to look at what he's done in the last year to prove that to you.
The Democrats are the party who has historically done more for those who are not wealthy than the Republicans. We now, better than ever, understand your views, and this is what we are going to do if elected to prove that we are on your side..."
Sadly IMO it'll be a case of tl;dl
The member of the electorate will say "Can you get me my well paid job with good benefits* back ?" and unless the answer is "Yes" then they will vote GOP - who will tell them what they want to hear.
* - The reason that job paid well and had good benefits was union representation, but they've also been convinced that unions are bad