You always have the Command spell prepared.
As a Bonus Action, you cast Command without expending a spell slot, and you take on an unearthly appearance for 1 minute or until your Concentration ends. During this time, you can cast Command as a Bonus Action without expending a spell slot.
Any creature Charmed by you automatically fails its saving throw against the Command you cast with this feature.
Once you use this feature, you can't use it again until you finish a Long Rest. You can also restore your use of it by expending a level 3+ spell slot (no action required).