Yoon wants to make changes to the Constitution if he is reinstated and the changes are made he will step down:

Impeached President Yoon Suk Yeol said Tuesday he will focus on revising the Constitution if reinstated, suggesting he could step down before the end of his single, five-year term.
Yoon made the remark in his final statement before the Constitutional Court, which is expected to deliver a ruling by mid-March on whether to uphold or dismiss his impeachment over his short-lived imposition of martial law in December.
“I will gather the will of the people and swiftly push for a constitutional amendment, doing my best to produce a Constitution and political structure that fit the changes in our society,” he said during the final hearing of his impeachment trial at the court.
“If a constitutional amendment and political reform are pursued correctly, I believe the separated and divided people will unite in the process,” he said.
“If that happens, there will be no reason to cling to the remainder of my term as guaranteed under the Constitution, and if anything, it will be a great honor,” he added.
South Korea’s Constitution limits presidents to a single, five-year term, but Yoon’s remark suggests he could accept calls to change the limit to two four-year terms and apply the rule to himself.
You can read more at the link, but this seems almost like a last effort hail mary in order to sway the court to not uphold the impeachment.