Follow this guide to create and export your glTF files:
Export all your variations to zip files:
When you create a new product in Plattar, choose the 'I have separate variations' option.
This will create a blank product for you to work with. Add a title/thumbnail to your product. Select your blank variation and 'Add model file'.
Add one of the zip files you created in the earlier steps. Click 'Add Variation' and add the rest of your zip files if you have any.