I am assuming all the computers were pulled out of the presidential office as part of the martial law investigation. Additionally all the prior personnel that worked there were reassigned to other areas of the government when President Yoon was impeached:

President Lee Jae-myung on Wednesday jokingly pointed out the lack of preparation for the handover by officials of the previous administration, saying that there was nothing prepared at the presidential office in Yongsan-gu, Seoul.
“I just came to the Yongsan office, and it’s like a graveyard. There’s nothing, not even an employee to give me something to write. No computers, or even printers,” he told reporters on his first day as the new leader of Korea.
Announcing the first batch of key nominations for key members of the administration, he stood where his predecessor Yoon Suk Yeol stood on Dec. 3 to declare martial law, which ultimately was his downfall from the leadership position.
He joked about how the presidential office, which had ceased function after the parliament impeached Yoon on Dec. 14, did not have any system for him to sign off on key documents.Kang Yu-jung, the spokesperson of the presidential office, told reporters later that it had been “physically impossible” to conduct work at the presidential office on the first day. She said the office lacked basic infrastructure and tools such as an internet connection or even pencils and paper, not to mention that the previous administration did not leave transition instructions for the incoming administration.
You can read more at the link, but according to the article the personnel reassigned after Yoon’s impeachment have been asked to return to work at the presidential office. Addtionally the article says that Lee Jae-myung expects to move the presidential office back to Cheongwadae in the next six months.