What is the procedure for considering promotion in state government?

Sir, my husband working as an assistant engineer in kerala gov. Harbour engineering department at now. He get this job by KPSC , it's main rank list his position is 2nd in sc category otherwise in the whole list he placed in 7th position. But in the joining date he extended for 6 month from the exact joining date, because that time he was pursued M.Des in IIT Bombay. So he gave the letter to Gov. for sanction the required leave for compeleting the course and they also allow the leave. Now the department upload the final gradation list , on this list his position goto 40th by the order of joining date . Sir my query is , if the promotion will proceed on the basis of gradation list, my husband promotion will considered after whole candidates. What we can do for change his position into previous place. It's for his lawful justice, because he get the higher rank in the recruitment . Kindly I requested to you give a suitable advise. Thank you.