Editing vertices

If I create an object, for example a plane, how could I change, for example, one vertex’ position.
Lets say it has to move up, from 0 to 1, while the other vertices stay on 0.
Is this possible, I searched online but I couldn’t find an answer.
Thanks in advance.

You need the vertex index so you can access in the mesh.vertices array.

int vertexIndex = 12;
Vector3[] vertices_temp = mesh.vertices;
Vector3 vertex_new = vertices_temp[vertexIndex];
vertex_new.y += 1f;
vertices_temp[vertexIndex] = vertex_new;
mesh.vertices = vertices_temp;