Yes, you can do this through CS Link.
After logging in, click on your account number on the Account Summary page. From here you can click ‘Make a Payment’ to make a partial early settlement of up to £999.
Please note, we will pay the partial early payment into your account, work out any rebate to which you may be entitled, and also apply this to the account. We will write to you in 10 days to advise you of your new regular repayments.
If applicable, your partial payment will be applied firstly to pay off any arrears, late payment interest and charges, before being applied to partially early settle your account.