He went to a fortuneteller and is asking whether he can repent and how he may repent?

Firstly: 

We praise Allah for having guided you to repent, and we ask Him to bless you with steadfastness in adhering to the truth. 

Secondly: 

The ahaadeeth of the Prophet (peace and blessings of Allah be upon him) clearly state that it is forbidden to go to soothsayers and fortunetellers. See question no. 8291. 

But not everyone who goes to a fortuneteller or a soothsayer is a mushrik in the sense of major shirk that puts one beyond the pale of Islam. Rather going to a fortuneteller or soothsayer falls into different categories. It may be major shirk, or it may be a sin, or it may be permissible. 

Shaykh Ibn ‘Uthaymeen said: 

Those who go to fortunetellers fall into three categories: 

1 – The one who goes to a fortuneteller and asks him things without believing in what he says. This is haraam, and the punishment of the one who does that is that his prayers are not accepted for forty days, as it is narrated in Saheeh Muslim (2230), that the Prophet (peace and blessings of Allah be upon him) said: “Whoever goes to a fortuneteller and asks him about something, his prayer will not be accepted for forty days.” 

2 – When a person goes to a fortuneteller and asks him about something and believes what he says. This is disbelief in Allah (kufr), because he is believing the fortuneteller’s claim to have knowledge of the unseen, and believing a human’s being claim to have knowledge of the unseen constitutes disbelief in the verse in which Allah says (interpretation of the meaning): 

“Say: None in the heavens and the earth knows the Ghayb (Unseen) except Allah”

[al-Naml 27:65].  

Hence it says in the saheeh hadeeth: “Whoever goes to a fortuneteller and believes what he says has disbelieved in that which was revealed to Muhammad (peace and blessings of Allah be upon him).” 

3 – When he goes to a fortuneteller and asks him questions so that he can explain to the people what he is really doing, which is deceiving people and leading them astray. There is nothing wrong with this. The evidence for that is the fact that the Prophet (peace and blessings of Allah be upon him) went to Ibn Sayyaad. The Prophet (peace and blessings of Allah be upon him) thought of something to himself.  The Prophet (peace and blessings of Allah be upon him) asked him what he was thinking of and he said, “Al-dukh” meaning al-dukhaan (smoke). End quote. 

Majmoo’ Fataawa wa Rasaa’il al-Shaykh Ibn ‘Uthaymeen, 2/184 

Based on this, whoever goes to a fortuneteller or soothsayer and believes what he says and believes that he has knowledge of the unseen has committed major kufr which puts him beyond the pale of Islam. But if he does not believe what he says then he has not committed kufr. 

Whatever the case, the door of repentance is open, as the Prophet (peace and blessings of Allah be upon him) said: “Allah will accept the repentance of His slave so long as the death rattle has not reached his throat.” (3537) 

i.e., so long as the soul has not reached the throat. Every sin from which a man repents, Allah will accept his repentance. Allah says (interpretation of the meaning): 

“Say: O ‘Ibaadi (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allah, verily, Allah forgives all sins. Truly, He is Oft‑Forgiving, Most Merciful”

[al-Zumar 39:53]

Whatever sin a person falls into, if he repents from it, his repentance will be accepted – even shirk. 

See question no. 9393. 

The basic principle is that the kaafir – and also the apostate from Islam – is required to utter the Shahaadatayn in order to enter Islam. If your going to the fortuneteller falls under the second category mentioned above, then you must utter the Shahaadatayn. As you have repented and started to live aright, you must have repeated the Shahaadatayn many times, so now you do not have to do anything. But you must resolve never to go back to such things again. 

And strive to acquire knowledge so that you may worship Allah with understanding. 

We ask Allah to help you to do that which He loves and is pleased with.