There are 3 ways to do this:
1) Using a promo code
Create a promo code with the discount you want and either book the client with this code or send it to them so they can book themselves.
Each user can use a promo code only once, but from the admin side, you can apply it as many times as needed.
2) Adjusting the order amount
Go to the Orders section and find the paid class.
On the right, in the Actions column, click the three dots (…) and select Adjust Amount.
3) Using a pass, credits, or a make‑up session
In the client’s profile, add 1 entry or the corresponding number of credits at the amount you choose (it can even be 0).
Then use this to book the class.