I presume the swelling is at the angle joint of an elbow. I fear that the damage has already been done. Most probably the MDF board or if it is an old top chipboard has gotten wet and swollen. If the joint can be completely separated it is sometimes possible to gouge the swollen wood out from the bottom with a router up to 1/4" from under the laminate and fill the straight edged cavity with more MDF, then heat and clamp with a flat board until the formica has cooled and stays in the flat shape. Then the joint can be redone properly. Almost certainly due to original sloppy cutting of joint edges.
Afraid this is a job for a tradesman or a very very handyman. Unless you know someone, the cost would not warrant the repair.
If the top is under two years old and has been installed professionally, you may have some come-back from the manufacturer/installer.