Since Boom is a small town close from both Brussels and Antwerp, the best way to get to Boom would be to land at either cities since they cater to major airline carriers.
From either Antwerp or Brussels, you could then either rent a car and drive to Boom or take a train that runs through Boom and stops there long enough for you to get off the train.
If you’re coming from the neighbouring countries or cities of Boom, you could check for bus or train services; don’t expect any of them to have a final stop in Boom since it’s a small town, but there will be buses and trains that will make a halt here.
HOW TO GET AROUND BOOM
Since Boom in a tiny little town most of it can be covered on foot.
If you’ve driven in to Boom, you could use the same car to get around.