Singapore's Multi-Ministry Taskforce has been closely monitoring the COVID-19 situation in the ROK. In view of the recent resurgence of new COVID-19 cases in the ROK, from 29 August 2020, 0000 hours, travellers entering Singapore with recent travel history, including transit, to the Republic of Korea within the last 14 days will be required to serve a 14 day Stay-Home Notice (SHN) at dedicated SHN facilities instead of their own place of residence. They will also need to undergo a COVID-19 test before the end of their SHN, as is the current requirement.
MOH's Press Release can be seen here: https://www.moh.gov.sg/news-highlights/details/updated-border-measures-for-travellers-from-the-republic-of-korea