These shares will already be in your Demat account.
Yes, you have to use RE’s recieved to apply for rights shares. When you apply for rights shares you will have to pay Rs. 55 per share.
Process to apply has been explained above.
How to apply for the Aditya Birla Fashions 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 .