There's groups like Run for Something that recruit progressives to run for state and local office
A surprising number of potentially winnable seats are never contested. Let's show up anywhere and everywhere to fight back
If you're worried about Republicans messing with elections themselves, you also have the power to help there too by running for state and local offices. Elections - even for federal positions - are run by state and local officals not by the federal government
I also reccomend applying to the DNC here in addition to usernames link.
EDIT: Looks like the nationwide party portal has no open positions, better to check out state-specific sites.