This article explains how to customize what services are bookable online.
Click Manager and Services
Single-click the name of a Service to open the service profile, click on Online & App tab, change the Available online toggle to No, then click Save.
If you would like to keep the service online, but only for specific staff members, then you can do this by setting staff member's qualifications. To restrict which days the service can be booked online you could set the service as a Special Offer.