
make it not turn into a 3mf file i need a stl file

I think you may be misunderstanding something, either about SimplyPrint and our job in the 3D printing chain or about 3D printing in general.
Inside SimplyPrint you can use our slicer to produce something that the printer can print. Usually you take in an STL file or any kind of 3D model, then you slice it and that pumps out a G-code file or sometimes a G-code file inside a 3MF file that is then sent to the printer. SimplyPrint does not contain any 3D modeling software.
Now in our slicer you may be able to export given objects on the build plate as an STL so you can’t do that. Beyond that I don’t think this request makes a lot of sense and I think it’s better put in our support or made more concrete in a new suggestion if I misunderstand.
