Help adding a variation type to existing listing with variations

Hoping you guys can help – I can’t figure this out and am a bit scared about messing up a decently-selling listing…

I have a listing that is both FBA and FBM (was set up as FBM and then added another item condition for FBA). The parent listing has a variation type of number of items – I sell these in 4- and 6-packs.

How do I add a variation types for a new type of the same item: color and/or shape? Once I selected and created the 4- and 6-packs, the other variation types are not available. There is a terse note under the “?” icon that says I need to delete this parent and create a new one, but there is no further info.

I’m not sure about the terminology, so finding a procedure is proving tough… Can someone help outline this process?