Show used slots

Hello,

I’m using your module « appointment hour booking » and I defined several services.
I do not succeed in configuring one option in « Field setting » tab for my services.
I checked the box named « Show used slots » but this is working service by service and not for all services.
I would like that all booked timeslots for all services combined are shown as used (and not only when I choose a specific service).
How can I configure my settings to do that?
Thanks in advance for your answer.
Best regards.