Thank you for your question. Unfortunately the reading, writing and listening for the CELBAN come together in what is called the Group Exam. For all of these skills (reading, writing and listening) the format of the exam is on paper in a room with other people taking the exam. For this reason they are grouped together. Speaking is different; the individual examinees sit in a room with two assessors. For this reason the speaking component is separate.
So you will have to take all three components together, again.
Depending on your jurisdiction, you may also be required to take the speaking again too. This depends on which province you live in; some provinces require the exam score to be from one sitting, others do not.
But you can take CELBANPrep writing separately.
Please note, people who have passed skills previously have been known to fail it when taking the exam again. For best results make sure you are preparing for the entire exam.