After you have submitted your application to the company, we are unable to edit your submission to include anything extra. This also applies for all candidates - once your application has been submitted, no changes can be made.
If you have submitted your application and forgotten to include something, we would recommend you to wait until the employer gets in touch, at which point you may be able to send additional documents.
Alternatively, you are also welcome to create a second account with StudentJob to re-apply for the vacancy. If you have any questions in regard to this, please do not hesitate to get in touch.