When creating a New Reservation (see How do I create a new Reservation?), or moving an existing Reservation (see How do I move a Reservation?) rather than selecting an available time slot, select the Enter Manually option

Tap on the Date and make your selection from the Calendar

Tap OK

Tap on the Time and enter a time using the Clock

Tap SAVE and then CONFIRM

Please note: This option disregards system calculated availability and allows double-booking. The double-booking will appear on your Booking page as below: