Including a Private IGCSE exam in the UCAS Application

I'm applying through UCAS, and in the education section there's a choice for different schools/centers. So I've completed all but one of my IGCSEs at school, which is Additional mathematics, which I've written privately. So, how would I go about including this in the qualifications?

Btw the test center I wrote it at (British Council Singapore) isn't on the dropdown menu when I search for it.

In the "School/college/centre name" drop-down list, select "My school/centre is not listed here". Then enter "British Council, Singapore" in the box provided.

The "Exam centre number" box would normally auto-complete if you were able to select your exam centre from the list. However, as you've had to enter the centre name manually, you'll need type the centre number manually too - directly in the box. If you don't know the centre number, contact the exam centre itself and check. (I believe it's SG003 but please check.)