The process has been explained here
How to apply for the Shriram Transport Finance rights issue?
Once you either receive the REs from the company or purchase it from the market, you will need to apply for the rights shares using Netbanking ASBA. You can check the process in this post . You can verify your entitlement on the website of the Registrar & Transfer Agent . The website will not be live until the issue opens.
You will need to enter your demat account’s Beneficiary Owner ID which is a 16-digit number while applying either on the RTA’s website or through your bank.