Repentance of the Fornicator

Assalaamu'alaikum.
I have a friend. He has married. He told me, someday he did 'Zinnah' with other woman. Now, he want to Taubat An-Nasuha. The Questions are :
How can he do a Taubat An-Nasuha ? Would be Allah 'azza wa jalla receive his Taubat ?
He told me, (I'm sorry if sounds rough), his penis did not entered to the woman's vagina, but their condition have been nude. His penis position between her up leg. Could we say that is a zinna that must be punished with 'rajm' ?
As information, In our country, the zinna can't punish with 'rajm'. I need your answer soon as possible.
Jazzakumullaahu khoiran katsiran.
Assalaamu'alaikum warahmatullaahi wabarakaatuh.

All Praises are Due to Allah

The act that your friend committed is a great sin and crime. He must repent to Allah. The Prophet (peace and blessings of Allah be upon him) said: "the eyes fornicate, the hands fornicate, the legs commit fornication, and the private parts commit fornication". (It is reported by Ahmad and it is in sahih Al Jahni 4150.)

Tell your friend that he has to increase in good deeds so that Allah will wipe out his evil deeds, as Abdullah ibn Masud reported. He said that a man came to the Prophet (peace and blessings of Allah be upon him) and said, ‘Oh Messenger of Allah (peace and blessings of Allah be upon him), I met a woman in the garden so I pulled her close, fondled her, kissed her, and did everything with except have intercourse. The Prophet (peace and blessings of Allah be upon him) was then silent and so the verse came down, "verily, the good deeds erase the bad deeds, that is admonition to those who remember." So the Prophet (peace and blessings of Allah be upon him) called him and recited it to him. So Umar (may Allah be pleased with him) said, ‘Oh Messenger of Allah (peace and blessings of Allah be upon him) is this for him specifically or for everyone. He said (peace and blessings of Allah be upon him) , ‘no, for everyone.' (It was narrated by Ahmad.)

There are more details on repenting from fornication. Refer to question #624. As for your question regarding whether he is considered to have committed fornication, which is punishable by stoning, it is obligatory that the married fornicator be stoned and the unmarried fornicator receive lashes. This is only if the sexual organs of the fornicator penetrate the vagina of the woman. Whatever is similar deserves a different punishment, depending on the level of the haram committed. It is not obligatory that he admit to a judge what he did. It is sufficient that repentance take place between him and Allah, and Allah is the Acceptor of repentance and the Most Merciful. We ask Allah to forgive us and the rest of the Muslims.

Allah knows best.