There are a bunch of great leftist Democratic candidates running for office all over the country. Help get them elected. That will push a Biden presidency in a more progressive direction.
Start with progressives in tight races who might turn a red district blue, like @DrCameronWebb in VA-05. https://www.drcameronwebb.com/
You could also support Candace Valenzuela ( @candacefor24), an awesome, tough candidate who could turn a GOP seat in Texas blue. https://candacefor24.com/
Then there's Carolyn Bourdeaux ( @Carolyn4GA7), running for an open seat in Georgia that had been held by a Republican. She's endorsed by Stacey Abrams and is blistering in her attacks on Trump and the GOP. https://www.carolyn4congress.com/
Check out Betsy Dirksen Londrigan ( @BetsyforIL) in Illinois's 13th District. She's really strong on gun laws and women's health issues. She barely lost to the incumbent Republican in 2018. https://www.betsydirksenlondrigan.com/