If you want to preselect service category to so that your customers can only see services that belong to this category, you can simple set selected_service_category attribute of the [latepoint_book_button] shortcode with a list of category IDs you want to appear on the booking form. You can find service category ID on categories list page in admin:

Example Usage:
[latepoint_book_button selected_service_category="25"]

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