You can use feed rules in Google merchant center, here is a guide: https://support.google.com/merchants/answer/7450276?hl=en
products > click on your product > choose the drop down more actions > google shopping > add the custom data
Anyone still looking to do this you can use bulk product editor by Hextom, because our facebook store doesn't recognise collections we used it to tag all of our best selling products with "Custom Label 0" "Best Seller" and then used the filter in our facebook store to find all products with this custom label. We were then able to create the set on there.
We have no idea why facebook shop doesn't see any categories (collections) product types or gender... its strange and we arent getting any help from anywhere about it.
Each data feed solution has different options. The Shopify one is the most basic.
For example my application allows you to pull in option values which in most cases is colors and sizes, and map it to the correct value.
Here is a great explainer: https://feedarmy.com/kb/map-shopify-apparel-values-to-google-merchant-using-feedarmy/