The antonym for replenish is ‘deplete’.
To replenish means to fill something up again or to restore it to its original state. For example, when you replenish your water supply after a hike, you are adding more water to it. On the other hand, to deplete means to use up or to reduce something to the point where it is no longer available. When you deplete your resources, you are exhausting them.
In essence, while replenish focuses on adding and restoring, deplete emphasizes the act of removing and using up. Therefore, these two words represent opposite actions in terms of the availability of resources.