Applying a Student Discount to an existing Premium account ?

[sianiedotx]

I have had a Premium account for 5 years.
For the last 2 years, I have also had the UK student discount, reducing the cost from £9.99 to £4.99.
Last month, my cost increased from £4.99 back to £9.99 again.
I'm still a student, so how can I apply my NUS Extra or Unidays discount again this year ?
The NUS Extra or Unidays sites only seem to be able to give the discount, if you are applying for a new Spotify account.
Is there a way to apply either of these discounts, to my existing account ?
I have had a look around this forum, but can't find an answer.
Thanks in advance 😉