The king stated that a decree written in the king’s name and sealed with the king’s ring could not be revoked (Esther 8:8). Instead, Esther and Mordecai were authorized to write another decree and seal it with the king’s ring (Esther 8:8).
In Esther 8:7–8, the king reminds Esther and Mordecai that he has already punished Haman and transferred Haman’s property to Esther because of Haman’s attack on the Jews. Yet the earlier royal order still stands, and the king says it cannot simply be canceled. These verses sit in the “reversal” section of Esther, after Haman’s exposure and execution in chapter 7 and after Mordecai’s rise in 8:1–2. Esther has just pleaded with the king to stop the harm planned against her people (8:3–6).
Esther 8:7–8 shows royal power working through paperwork: the king has already punished Haman and transferred “the house of Haman” to Esther, but Haman’s earlier sealed order still stands. The king therefore authorizes Esther and Mordecai to create a new written instruction “in the king’s name” and to seal it with the king’s ring.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Esther 8:8, then read the surrounding section so the answer stays connected to the passage's flow.
8Write you also to the Jews, as it pleases you, in the king`s name, and seal it with the king`s ring; for the writing which is written in the king`s name, and sealed with the king`s ring, may no man reverse.