apple imac G3+ degaus

i was geven an old apple work decent for a while then the hard drive crashed and i think the degausing coil may have failed. because the monitor (CRT) cow is smaller than it should be it has black around the edges and the part that is showing has a outward curve in the center of the L/R sides. i looked it up it soundsl ike ther're suposed to dagause at boot. but has no afect. i have a old electromagent ment to erase old vidio and audio tapes. thought about trying to use that to do it but dont know how and afiad it may make it worse. (i beleve this is a degausing isue). havent seen setings to adjust that made any diference with the problem.

 

ok is there some way to adjust this? if i remember from working on crts there seems to be potometoers on the flyback and some on the board or is there some program that can do this? seems odd how it would just start this all the sudden if that was the problem. thats partily why i thought it may be degause.