Molar management

I brush my teeth diligently in my own way.

It seems that the toothbrush doesn't reach even the molars properly.

My molars decay easily. I brush diligently, but still.

I'm upset because I have a cavity in my molar.

How do you manage molars located deep inside? How should I care for areas that are hard to reach?

I'm worried. When I go to the dentist, the nurse tells me to take good care of my molars.