2017 Year-end tax settlement data at the Hometax will be ready from Jan.15, and you can download all of deductible items there and submit it to your employer.
And your employer need to issue you a receipt(연말정산 원천징수 영수증) for you.
Actually your employer need to file those record by the 12th of March electronically.
I think your employer already released the schedule and asked a necessary documents list for the settlement.
Please hit the below website for more details on this settlement.
You can amend those filing which is done by your employer by the end of May for confirmation.
So if any doubt, please send me the receipt(원천징수영수증) which is issued in the February to me for review and I'll take care thereafter.
Always to firstname.lastname@example.org.