Always wear goggles or protective glasses when sanding any kind of wood to prevent dust from getting into your eyes.
Sand the swollen area with 220 grit sandpaper. When finished sanding the swollen area, the entire table top will need to be sanded as well. You will use several sanding disks to completely sand down the table.
After sanding, your coffee table will be even. If it's not as even as you would like, mix bleach with water into a bucket. Scrub the entire coffee table with the solution, focusing on the stained and (once) swollen area.
Allow the table to dry completely, then sand the surface once more.
Apply furniture oil to the entire coffee table. Continue adding coats of oil until you are pleased with the depth of the color. The oil will even the color of the table.