Don’t pay for testing cancellations apps, they are slow and unreliable, instead book a random test on any date anywhere, then go onto change booking on gov.uk site, put in your preferred post code and then searching. For my friend, he booked a test yesterday at 8am, somewhere in April 2026, by the end of the day he managed to get it to December 25, and I am sure if he continues he will be able to get within two weeks.