How to Prune keeled garlic?
No pruning required, other than to remove old flowered stems and foliage

keeled garlic · Allium carinatum subsp. pulchellum
Grow in full sun and fertile well-drained soil. It is best to grow in containers where garden soil is heavy clay and prone to saturation over winter. Rapidly forms clumps but is not a nuisance. See allium cultivation
No pruning required, other than to remove old flowered stems and foliage