Before the file format is criticised again:
In PrusaSlicer you can open or import a 3MF file. There is a difference. If you open a 3MF you will also load the print settings from the file. (Not needed here. It would load the defaults of the Prusa Mini.) If you import a 3MF you just load the contained models.
The models in these files are already split into individual objects. Just delete what you don't need and add instances of what you need more.
The author marked this model as their own original creation.