Verification by quantity of NFTs held.
When setting up roles based on the number of NFTs held you are going to select this option in your setup dropdown menu.
Once that is selected add the OS collection link to the project you are verifying with.

Selecting upper and lower bounds

Quantity is set by upper and lower bounds through Vulcan. For example, if you want grant roles with users who own 20 NFTs and above you'd set lower bounds to 20 and upper to 10,000+ or whatever the full collection size is.
Once that's saved you're ready to go. Below is an example flow.