How to prioritise one set of customers to book event.

[Farooq-UK]

I use a multi-bookings event published on my Microsoft bookings page for an exercise class. The number of spaces available are restricted and for the most part this works well. However, the multi-booking event is open to all my customers, and given event has restricted number of places, I would like my oldest customers who have been with me from the beginning to have priority or opportunity to book before all the rest. How can I achieve this? How do I give them (original customers) opportunity to book before everyone else? Would welcome any help of suggestions with this issue please!
Thank you in advance.

[#2]

You could setup a new bookings calendar for the event, and email it first to your most loyal customers, adding encouragement that they have priority access to register for the event. Then email the URL to the rest of your customers.