Paying towards 24 Month Instalment plan using money in paypal wallet

[personage]

Hi, i'm paying for a computer using paypal credit 24 month plan. I want to pay towards it with my paypal balance how would i do that.

It says to go to wallet - paypal credit - make a payment, but theres nothing there in current balance and other just has a text box.

Just want to pay a bit towards my plan so i can pay it off early.