What is the religious ruling regarding a man who committed the abomination of Zina in his youth, then repented and got married, and if he wishes to apply the Hadd, where should he go to have it carried out?

If you repent with sincere repentance, then Allah accepts repentance from His servants; in fact, He transforms evil deeds into good ones. You are not required to inflict the punishment upon yourself; rather, it is obligatory for you to conceal yourself with Allah's concealment.