What should one do who made a mistake in the last tashahhud and then said the taslim?

The final Tashahhud is a pillar (rukn) of prayer according to the Shafi'i and Hanbali schools, and any authentically transmitted form suffices, such as the form narrated by Abdullah ibn Mas'ud. Whoever omits a single letter from the Tashahhud, their prayer is invalid according to some scholars. Lahn (grammatical error or mispronunciation) in the Tashahhud, if it does not intentionally change the meaning, does not invalidate the prayer. However, if it intentionally changes the meaning, the prayer is invalidated and must be repeated. If the error is intentional but does not change the meaning, the prayer is valid based on the preference of some scholars.