Orientation of printing area in 3D-model

Hi,

I am having issues with the correct configuration of my custom 3D-model.

I have purchased a 3D-sample and created my model accordingly.

The customization is visible in the 3d-model, but it is rotated by 90° and mirrored. I have been trying to change the orientation of the vertices but with no success so far.

Can someone point me into the right direction? Support has not been helpful so far, they only support custom 3D-models in paid jobs.

Thanks!