If his name is not in the assist portal system and only being registered now, then refund fully.. U cannot backtrack.. But if he is, back pay everything... Penalties should be around 6% per annum or if anything lesser than rm5, then rm5 is charged for every month..

Back pay for all the previous month, else he will not be able to claim EIS shall anything happened to him ... As for penalty, Socso will calculate and let you know... You can always contact Socso and let them know your issue and why miss out on contribution