First, open TaleWeaverLite and load your previously made creature mod file

Near the save button at the bottom of the panel, click the "EXPORT FOR MOD.IO" button

There will now be a zip file that contains the tsMod file.

Extra context: The zip is structured as required by mod.io (you can't just zip the file, you need to put it in a directory and zip that), and the tsMod file is named "root.tsMod" which is what TaleSpire needs for zipped mods.

Done!

You can now go to https://mod.io/g/talespire and upload your creation!
Remember to tag is as a creature.