Excise rule 16

1.You have to intimate with Annex -I, to your Excise Range Office, 

2. If you have to avail cenvat credit on that retuen goods , you have to mention in Annex-I, and avail as Input cenvat credit,  condition to that invoice copy should be transporter copy of your customer or yours, 

Pls refere the below link :

https://centralexcisechennai.gov.in/chennai3/excise%20tradenotices/TN_2002/TN14%282002%29.htm

Earlier there were so many formalities but now this is very simple. There must be a rejection letter from the party and it should be accompanied with your invoice (duplicate for transporter copy) and LR from party to you. Take stock in your RG-1 and CENVAT in your RG 23 A Part II. And then if you have to make any process then do it and sale like a fresh goods.