There are two possible causes for your problem, one fatal, the other fixable. If the magnets are of average strength, they will have just imparted some magnetism to the aperture grille, and this can be fixed by degaussing. The screen. See you TV instruction book for how to degauss. With some TVs it's a menu option, but with my Sony it involves disconnecting the TV from the mains and reconnecting it (it's not enough to switch it off). When the degaussing circuit operates, you will here a loud sort of buzz, and the picture will wobble for a few seconds. You may need to repeat the operation a number of times to cure the problem.
The second possible cause, is that the magnets gave actually distorted the aperture grille (they are very fine and delicate). If this is the case, I'm afraid that the TV is now junk!