Large-scale tree planting can remove some CO2 from the atmosphere, but nowhere near as much as humans add by extracting and burning fossil fuels. See https://skepticalscience.com/1-trillion-trees-impact.html for a detailed assessment of what this looks like.

The IPCC has a chart showing what actions need to be taken over the next few years. Afforestation is one piece of many things, all of which we need to do.