Do normal dentist help with treating and reducing lip fullness?

No: By normal i assume you mean general dentists. Usually lip fullness reduction can be treated surgically by a facial plastic surgeon. If the lip fullness is caused by tooth positioning, an orthodontist would be the answer.

Lip fullness: If the fullness is not related to tooth position, then consult a plastic surgeon if it's bad enough and important enough that you feel it requires treatment. If it is due to tooth position such as with a malocclusion or poorly made denture, veneers or crowns, then consult a general dentist, prosthodontist or orthodontist as necessary.