Under K1 visa section on the US Consulate Seoul page:
Step 2: Schedule the Interview
Once the U.S. Embassy Seoul receives the approved petition from NVC, the Immigrant Visa Section will send you the Instruction Package by e-mail, with a list of the documents the intending immigrant must present at the immigrant visa interview.
Note: Do not schedule your interview date until you receive these instructions. If you do not receive the instructions from the US Embassy within two months after the notification from NVC about the transferring of your case to Seoul, you have to send an inquiry about the status of your case to the call center at support-southkorea@usvisascheduling.com . Please be advised that you might have submit a new petition if you do not schedule an interview within four months of petition approval.
https://ustraveldocs.com/kr/en/immigrant-visa/