Scaling, how to have 3d model in real dimension

[S-Alireza-R]

Hi. Thanks for providing this model. When I got a 3d model of some objects to use for a 3d printer I found that they were in smaller sizes than the real one. How to fix it and Have the model in scale?
The five cm object was converted to a 2-3 mm 3d model.
I want to do it manually but I figured out that the model could do it but I don't know how.