DCM file (change color map) It may too basic to you. help me!

I know this question can be very basic and cumbersome.
But using 3d slicer in windows, I’m having a lot of trouble trying to convert the surface changes to color maps.

I converted dcm files to stl file.
and I want to make a color map in surface change.

I would like to know if there is any way to convert stl file to vtk file.
Lots of guideline tell us it begins with vtk file.
but I cannor find a way to make vtk files.

Please tell me how to change dcm file to vtk file.

Your answers will be of great help to my research.

Thank you.