Hi!
I recently watched a Kurzgesagt video on YouTube, that adressed this topic.
One of my favorite methods of Geoengineering they mentioned, was fertelizing the oceans with iron, so that the growth of algae would be increased. Why the increased growth of algae would be benefficiary, is pretty self explainatory.
They did mention other methods aswell, but this one sticked with me the best. I would recommend it, if you wanna look more into this topic