Increasing the biomass of trees (e.g, growing a new forest) does reduce the CO2 levels; true, each tree in this forest will at some point die and re-release its carbon, but another will grow in its place; therefore, if the forest has grown and stays there forever the the result will be a net negative contribution to CO2 levels forever as well.
That of course does not change the fact that carbon offsetting alone is NOT a sufficient way to tackle climate change. Please do reduce your carbon footprint people, and encourage others to do so. Of course, there's nothing wrong with planting trees in addition (not instead of) reducing your emissions - you can think of it as charity for the planet; if you're interested in donating money so that forests get protected / grown, I recommend Stand For Trees: https://standfortrees.org/en/#protect-a-forest (I'm not affiliated with them).
Please people, be careful about what you write on these topics. We really need a high bar on scientific rigour on these topics if we are to act effectively.