If you’re a US citizen, no matter where in the world, start by making sure you’re registered to vote. Many districts are gerrymandered, so you’ll want to register as the party that’s likely to win congressional and/or state legislative districts where you live, and vote in that party’s primary.
In addition to voting, you’ll want to influence politics beyond that. Your local races are a good place to start; cities and states control local land use and things like building codes.
For President, the reality is that Biden has done far more than Trump would even consider, starting with the Inflation Reduction Act, and continuing through numerous executive actions. Getting involved in this race means volunteering, and if you can, donating to the Biden Victory Fund. If you’re giving really large amounts of money, and the logistics of it work, go to an in-person event and talk to the candidate or other official about climate: