You can't completely keep the doctor away by just eating apples but you can improve your health by eating apples which means you may not get as sick and not have to see the doctor as often.
But you still should see a doctor at regular appointments to make sure your health is in good condition and so you can catch any diseases or problems early on through blood tests etc.
So you can have better health while eating apples but eating apples everyday won't actually keep the doctor away 100%.
When my mom told me that years ago as a kid I started eating an apple per day because she said it would keep the doctor away.
But that was a lie I still was forced to go to the doctor even after eating those apples.