[protonatedalkene]

its corresponding enantiomer?

I believe that you just swap the coordinates of two of the 4 atoms that are attached to the stereogenic carbon (or other element), but I am not sure.

Any help?

[Irlanur]

mirror

[AWK]

General case:
For molecule Cabcd (where a,b,c & d are substituents at chiral C atom) you can reverse signs all coordinates of all substituents.  Then a new molecule is related by a center of symmetry at 0,0,0.
or (special cases)
Orient molecule in plane a (plane y0z) - in such a way that any two substituents and C atom lay on the plane. Then reversing signs at x coordinates for other two substituents gives you the second enantiomer (mirror plane);
analogously
plane b (x0z) reverse signs of y coordinates for other two substituents
plane c (x0y) reverse signs of z ...