How to add variants from fabric library to patterns?

To start with, in Fabric Library, each fabric is unique and you can add colorways by using the Color Option. Fabric Library is a center for managing and organizing fabrics based on SPU. Therefore, you cannot add fabric variants from the fabric library to a pattern directly.

However, that does not mean adding variants to patterns is not possible.

Go to Block Library, and upload a block as you normally do. Then go to the 3D editing page of the single block you've uploaded, and click the "Fabric" icon and select fabrics from your library to add variants to patterns.

If you want to share the fabric and its variants with your clients, you can create a fabric collection in Application Center. Go to Collections and click "Add" to create a new collection. Then choose the product module. Click "Link" to add fabrics to your collection. Select fabrics or the variants and then confirm. 

Once you create a collection, you can share it with others as per you needs.