I don't brush my teeth enough i have cavities and now the inside of my tooth is black and wont go away how do i fix this without going to the dentist?

No way to fix: Need to see your dentist for evaluation and treatment.

You can't: Fix it on your own. You need to see a dentist. You need to start brushing and taking care of your teeth or you will loose all of your teeth soon.

Dentist: Self treatment is limited to prevention. You must see a dentist for repair. The decay you have will get worse and you'll be looking at extractions.

You cant: Once you have cavities, they only get worse unless you seek professional care. Seek treatment as soon as possible before your situation gets worse.