Cutting a shape from mesh Mesh Deformation

Hi there I hope you are well I stuck at mesh deformation. I am trying to cut a shape from a mesh with mouse input like that image on the below but I dont know how to achieve that .My main reason for do this is I want to cut a shape from that mesh then I want to save that cut part as a new game object .Currently I am searching about mesh deformation in unity but I dont how can achieve this. Could you help me what should I do or do you have a any tutorial document about this Thanks=)