Hello,
Sorry for the delay. I think the only possibility is if you ask a ticket stop shop whether they can do it. I don’t know for sure, but they might be able to. Ticket machines will only allow multiples of 5p or 10p. Online it’s multiples of £5.
The only other way to get the balance back is to refund the card, but if you needed another one it would now cost the £7 fee. Once refunded the old card is deactivated.