Whitch programme i shoud use to conversion

Hi there,

I have a little problem. I want to convert SKP and STL files into GLB file, for our website. We use the 3D viewer plug in to show 3D models. (https://www.ads-software.com/plugins/3d-viewer/)
We want to use open source converter but we don’t find it. Could you show what converter can we use?

Thanks in advance!