You have two options....
i) To try booking two fresh tickets from Kozhikode to Trivandrum, if confirmed booking available and then cancel the old ticket booking,
ii) To try booking two fresh tickets from Kozhikode to Thrissur City. (in this case you will have to do shifting at Thrissur as the sitting Nos. and coach will be different and may not be the same. However, you can do this on the train itself as coaches are interconnected.