Your question is not very clear -how has your tooth "turned into the shape of a cone? Teeth do not gradually change shape - did it chip or break somehow? If your tooth has become conical in shape, it is quite certainly broken. Chipping usually involves the breaking off of a tiny piece of enamel from the tooth. This is usually not very noticeable, and in many cases does not require any treatment. This however is a call that your dentist needs to take. In some cases, a chipped tooth will require some minor work. If it is rough or sharp and likely to injury you, the dentist will usually recommend filing the tooth till it is smooth again, or repairing the chipped portion using some suitable material.
In your case, the tooth does not seem to have chipped, but instead it seems that a reasonably large piece of your tooth has broken off. This quite certainly requires treatment; it is unlikely that the tooth can be filed down, so you will probably have to use a crown. This will roughly replicate the original shape of the tooth, protecting the tooth itself as well as your mouth. If the tooth is too badly broken, the dentist might suggest extracting it to prevent further damage.
answered by G R