There are many grassroots organizations, below are the ones Grayroots Movement recommends. Indivisible.org groups are all over the country, you can find one almost everywhere! Sisterdistrict.org is an organization for Democrats in blue states to help elect Democrats in red states, the same with adoptastate.org. and swingleft.org.
swingleft.org sisterdistrict.com indivisible.org
adoptastate.org knockeverydoor.org emilyslist.org