What must a young man do to atone for embracing and kissing a non-mahram girl twice during the daytime in Ramadan, knowing that he has made up those two days, and he seeks Allah's forgiveness?

A young man must repent to Allah the Almighty from the unlawful acts he committed, by abandoning the sin, regretting it, and resolving not to return to it. If his repentance is sincere, then there is nothing upon him, for a sound repentance is accepted and erases what preceded it. Regarding the Ramadan fast, if no ejaculation occurred with the unlawful acts, then his fast is not invalidated. If he did ejaculate, then he must make up for the fast, and since he has already done so, there is nothing upon him.