By which method of asexual reproduction an organism restores its lost body parts?

Asexual reproduction is a mode of reproduction in which the offspring is produced by a single parent. 

In some organisms, specialized cells called stem cells can repair and restore a severed body part. This process in which an organism restores its broken or lost body parts is known as regeneration. A few examples include Planaria, Hydra, starfish, etc.

Regeneration usually takes place in those organisms that have a very simple body design with very few specialized cells.