Hi @Penny71,
Unfortunately you are probably out of luck. A pre-approval is just an allowance to let someone book, but it is not a booking. You can pre-approve more than one person at a time, and whoever books first gets the booking, even if you pre-approved the other one first.
Airbnb penalizes hosts who cancel bookings in a few ways: blocking those dates for other bookings, ineligibility from becoming superhost for a year, and occasionally a monetary fine as well. This is to prevent discrimination.
I used to try to delay pre-approving a second person for dates I had already pre-approved for someone else because I felt bad, and thought they had the "right" to book, but now I don't worry. I just let them know that someone else is interested in the same dates, and then go with whatever happens.
If you ever need to book for an "extenuating circumstance" (flood, fire, serious illness), the penalties will be forgiven if you call the company. Even in those situations, if possible, it is easier to call the company and have them cancel.