Quick political science lesson. Political parties in the US are non-hierarchical.* That’s a fancy way of saying neither their candidates for office nor their platforms are determined by a central authority.
In other words, the DNC chair is not worth getting all worked up over. If you want to change the party, get some candidates who can win primaries for state legislative and congressional races. Oh, and make sure that said candidates also could realistically win the general election. That is all.
* As explained in Chapter 6 of A Different Democracy.