How does one have believe in God?

My probleme is that i wnated to become a believer but not a believer who just believes without knowledge and certianity .And i dont know why even though i saw the signs in the universe like the fine tuned universe and i still didn't become a believer so i realise that my mind is deluded and is not able to find the truth and has become irrational , as it is said in the quran that even if the disbelievers see the signs they deny and i am one of that,so how to come out of it and how to fix this irrationality of mind and i don't know why i don't accept the signs