If you look in the slicer there should be a black box on the back side of the print. I imagine thats where the hole is. You can now manually block or remove parts of the print with simple geometry.

On the back of the pig (Plate 2), there is a negative box on the plate. When you slice this Plate 2 with that negative, it will create a whole. You can check the Plate after you slice it to make sure the whole is there. You can also create your own negative in bambu studio, but it is not necessary since the poster of this STL already provided what you needed. If the whole is not big enough, you can size the negative square to any size you want.