The product information does not specify a strict frequency, so the right routine depends on your skin type and how it reacts. A reasonable starting point is once daily, for example in the evening, or every other day if your skin is sensitive. On days you do not use the bar, wash with a gentler cleanser and plain water.
Because the salicylic acid is rinsed off, it is less likely to cause dryness than a leave-on product, but it can still add up if you also use other exfoliating ingredients. Use it more often when your skin feels oily — after a workout or on hot days — and reduce frequency if you notice tightness, flaking, or stinging. You can also use it only on oilier areas such as the T-zone or back and use a milder cleanser elsewhere.
If you combine it with exfoliating acids, retinoids, or strong anti-blemish products, pay attention to how your skin responds and consider using the bar less frequently or on alternating days. Stop use if irritation appears and consult a specialist if you have concerns about a reaction.