Is there a way or a prayer to facilitate marriage to a specific girl after stopping an illicit relationship?

You did well to end the relationship with the foreign girl, because Islamic law guides those who love each other towards marriage, and it has commanded the exertion of efforts that facilitate it, such as the expenses of marriage, which are part of the "Baa'ah" mentioned in the agreed-upon Hadith: "O young people, whoever among you can afford the 'Baa'ah' let him marry." As for supplication, it is fundamental, and there is no specific supplication for marriage, but one can supplicate with general supplications that include asking Allah for success and facilitation. If marriage to her is not facilitated, then one can look for someone else, and love sickness can be treated. It is recommended to fast and do similar acts that promote chastity until Allah facilitates marriage.