What should one do who printed and published a fabricated story about a dialogue between Satan and the Prophet, which he had received from a mosque, and then distributed it to many people?

There is no sin upon you for what you did in distributing the fabricated hadith (definition), as long as you did not know it was fabricated, because Allah says: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended." (Quran 33:5) And because He says: "Our Lord, do not impose blame upon us if we forget or err." (Quran 2:286) And due to the hadith: "Indeed, actions are by intentions." In the future, you must verify and inquire about the authenticity of what you do. And part of completing repentance is to strive to retract what you distributed, along with clarifying that it is fabricated, to the best of your ability.