Is it necessary for one who distorted the Qur’an—and is remorseful for his action—to utter anything along with the Shahada?

Deliberately distorting the Qur'an is forbidden, rather it is disbelief (kufr). Consensus has been transmitted regarding this, and whoever intentionally omits a letter from it, or substitutes it with another, or adds to it, is a disbeliever. The repentance of one who distorts it is through uttering the Shahada and retracting what they did in terms of distortion.