Firstly, visit the official Trivandrum RTO website and fill and submit the ownership transfer certificate online. It should be done jointly by the seller and buyer. After the submission of the form both parties will receive the OTP on their registered mobile numbers to authenticate the request. Once everything is in order, you will have to submit scanned copies of required and supporting documents along with the signature on the duly filled application form. The whole procedure should be completed within a month of the transaction of the vehicle took place from old owner to the new one.