What kind of car do you have?

When your mirror glass turns yellow like that it means the wiring shorted out your heating element and smoked the mirror glass.

Sometimes you have to replace the whole mirror assembly if the wiring insulation is all deteriorated, unless someone else knows of a cheaper alternative.

You may get lucky, and the wiring is okay, and the heated mirror glass shorted and just needs replaced, but more info is needed on make , model, year of car.